Semiotics 2: What the hell is an index?

The topic of this post is to talk about the concept of an index in semiotics. Along with the icon and the symbol, index is one of the three main types of signs discussed in many introductory books that explain the basics of semiotics, but I've been struggling to really grok the meaning. Turns out that just as the books tend to say, different sources use slightly differing definitions for this word and this is fine. I guess this is obvious to anyone who isn't a mathematician. Wasn't for me.

Anyway, today our focus is on the index from the triplet of icon, symbol and index. Semiotical and sociolinguistical literature use the index in different ways, and in this post I think out loud while I try to figure out how to fit them together to a conceptual state I can ingest.

The basics

In semiotics, a sign is anything that stands for something else. E.g. a literal traffic sign, a word in a book, a wink from a friend, or a photograph. The traffic sign signifies usually some rule you should follow, a word in a book can signify some concept in the world the author wants you to think about, a wink from a friend can signify almost anything and a photograph of a person can signify that person. These meanings attached to signs are not inherent to them, and only come to be due to someone interpreting the sign.

The purpose of semiotics is to study how we (humans) attach meaning to these signs.¹ For example the following photograph² of Che Guevara is a sign that is often used to signify many other things besides the particular person in the picture. Indeed, I could imagine that for some people the photograph signifies Che, and then Che in turn signifies further things, but I can also imagine that some people don't even know who the person is and simply see the photograph as a sign for rebellion.

According to my very limited study of the literature, the founders of semiotics are often said to be the linguist Ferdinand de Saussure and the polymath Charles Sanders Peirce. Peirce in particular is credited from coining the triplet of icon, symbol and index. The quick idea is that an icon resembles something, a symbol symbolizes something not via resemblance but by (sociocultural) convention and index points to something through e.g. a causal or locational relationship.

We should note from the start that this division should not be considered a classification of things to distinct types. In practice any symbol combines all three of these types, and it might be better to think of these as color hues like red, green and blue. Most of the colors you see are mixes of these three. Though such color metaphor can also be misleading, as it might seem to imply that for each sign there is a unique representation of type in the form of "10% icon + 72% symbol + 18% index", which is not the case. Nor should this be thought to imply that "the space of all signs" would be three dimensional as "it can be described with three primary components/directions".

To emphasize that this is semiotics, not linear algebra, we note that Roman Jacobson has further suggested a division based on two "axes"; contiguity-similarity and factual-imputed which contains the triplet of icon-symbol-index:

	Similarity	Contiguity
Factual	Icon	Index
Imputed	X	Symbol

Here the missing "X" box is described by Chandler as follows:

[...] ‘imputed similarity’ to which Jakobson assigns ostensibly non-referential signs which nevertheless generate emotional connotations – such as music and non-representational visual art [..]

So a bad reading of this would be that the semiotical concept space is two-dimensional, with Jacobson having found the mapping between Peirce's three dimensional representation and this two-dimensional world. The situation is naturally much more complex, and even more crucially, it is very strongly dependent on the person doing the interpretation. The "conceptual space of sign contents" is not some independent abstract space to which various signs map to, but instead we always need to have someone³ who forms the meaning of a symbol. It feels like a huge understatement to merely say that "the meaning of a sign is very context-dependendant" - it really is, but it's not so much only dependent on the context but completely formed by the context.

Nevertheless, the definition of such three archetypes of icon, symbol and index have been very useful in enabling discourse on the topic of semiotics. To us this is the best sign of their importance, and does seem to imply that these are three particularly important dimensions that one might consider in a semiotic analysis. Scollon & Wong Scollon seem to agree:

"Icons, indexes, and symbols are the full inventory of the ways in which we can signal our meanings to others. To put it briefly, a sign can resemble the object (icon), it can point to or be attached to the object (index), or it can be only arbitrarily or conventionally associated with the object (symbol)."

My problem

At the surface level the definition of an index can be quite straightforward. In Semiotics, the basics, Daniel Chandler gives the following definition. If you are not familiar with the terminology of semiotics, here you can think "the signifier" as the sign and "the signified" as the thing that it stands for.

[...] the signifier is not arbitrary but is directly connected in some way (physically or causally) to the signified (regardless of intention) – this link can be observed or inferred: e.g. ‘natural signs’ (smoke, thunder, footprints, echoes, non-synthetic odours and flavours), medical symptoms (pain, a rash, pulse-rate), measuring instruments (weathercock, thermometer, clock, spirit-level), ‘signals’ (a knock on a door, a phone ringing), pointers (a pointing ‘index’ finger, a directional signpost), recordings (a photograph, a film, video or television shot, an audio recorded voice), personal ‘trademarks’ (handwriting, catch phrases).

Next we'll look at an example and start raising problems. For the sake of preserving in the exposition some remnants of my intellectual journey, we'll first list here various issues I've had, and then start solving them in a later section.

Rami and his berries

Here is a picture of me pointing at a particular berry out of many berries.

So here you could say that I am indexing the berry, and this would seem quite straightforward. But here we already start to run into a few details worthy of note. Let's go through these one by one.

Sub-problem 1: How does pointing work?

Is pointing really a universally acknowledged thing? To my understanding, humans and dogs tend to be the only animals capable of understanding it, though I am not sure of many primates, and even for humans it apparently is something we have to learn; in the language instinct Pinker writes as follows.

The psychologist Laura Ann Petitto has a startling demonstration that the arbitrariness of the relation between a symbol and its meaning is deeply entrenched in the child’s mind. Shortly before they turn two, English-speaking children learn the pronouns you and me. Often they reverse them, using you to refer to themselves. The error is forgivable. You and me are “deictic” pronouns, whose referent shifts with the speaker: you refers to you when I use it but to me when you use it. So children may need some time to get that down. After all, Jessica hears her mother refer to her, Jessica, using you; why should she not think that you means “Jessica”?

Now, in ASL the sign for “me” is a point to one’s chest; the sign for “you” is a point to one’s partner. What could be more transparent? One would expect that using “you” and “me” in ASL would be as foolproof as knowing how to point, which all babies, deaf and hearing, do before their first birthday. But for the deaf children Petitto studied, pointing is not pointing. The children used the sign of pointing to their conversational partners to mean “me” at exactly the age at which hearing children use the spoken sound you to mean “me.” The children were treating the gesture as a pure linguistic symbol; the fact that it pointed somewhere did not register as being relevant. This attitude is appropriate in learning sign languages; in ASL, the pointing hand-shape is like a meaningless consonant or vowel, found as a component of many other signs, like “candy” and “ugly.”

So the concept of pointing only works because the pointing finger is jointly agreed upon by everyone to mean what it does. But doesn't this make the pointing finger a symbol for the abstract concept of "the thing relevant to the situation you get if you imagina a straight line emanating from my finger"? (Or some abstract variations of this where pointing away just means "away from here" like pointing somewhere while shouting "Get the feck away from here!"?) Thinking about this for a while, doesn't everything indexical become a symbol now as they rely on agreed upon conventions? (Or at least any indexical things except of the "natural signs" that are direct causal relations like smoke signaling fire.)

Furthermore, doesn't every icon also require some context to be interpreted properly? For example even something very strongly iconic like a photograph of a person might mean the person in the picture in general, or the person at the picture at the particular moment the image was taken. Photographs are to our eyes very iconic partly because we have vast amount of processing power in our brains dedicated solely to preprocessing image data before it reaches our conscious mind, ignoring things like color errors or shadows and the like to bring to our mind an "image" that is most useful for our day-to-day lives. So the "resemblance" between a photograph and a person is not illusory per se (though see Hoffman), but it is not a physical fact either.

Sub-problem 2: How does this indexing really break down?

So in the picture above:

• I am indexing a berry.
• Or my hand is now a sign that functions as an index for the berry.
• Or that my extended pointing finger is a symbol that means the concept of "I want to convey the thing that I point at.", which then maps to the particular berry.
• Or the whole image functions as an icon representing the idea of pointing.
• Or I am actually pointing at the particular board, the berries just happen to be there, and you should replace "berry" with "board" in the interpretations above.

So which one is it? Or something else? Or all of them?

On the one hand, part of the answer is easy; it's all about the context. A carpenter who I am talking with about replacing a board will see this to mean that "this plank here". Someone else will get the meaning of "this berry here" out of this. You as the reader of this text will see the whole image as representing the idea of pointing - or not, you might of course interpreet this as something completely different like a sign of me not understanding semiotics very well.⁴

On the other hand, part of the answer here is not easy (for me). Especially the question about whether the pointing finger is an indexical sign for a berry or if it is a symbol that symbolizes the concept of a pointer. This is again the same issue I think about when looking at an image of Che Guevara; is this image a symbol of rebellion, or an icon of Che whose memory happens to be a symbol of rebellion? Or is Che Guevara perhaps an index of (the Cuban) rebellion?

Sub-problem 3: Indeces at the literature

While learning the basics of general semiotics, I've been also studying more particular topics like visual semiotics, general linguistics and geosemiotics. None of which I truly understand at the moment. All of these tend to discuss also indeces, but not in identical ways.

We run across the following concepts:

• an index (noun)
  • In the spirit of "natural signs" where an index needs pretty much causal connection to what it signifies.
  • In the spirit of "the arrow in this emergency exit sign is an index that points towards the location of the door".
  • In the spirit of linguistics where the so called deictic pronouns/terms (like "this", "that", "here", "now", "yesterday") are considered as indeces.
• to index (verb)
  • "A sign can index the sociolinguistical landscape." (Scollon & Wong Scollon)
  • People can index signs. (Scollon & Wong Scollon)

So here I go first reading that "a picture of a cat is an icon of a cat, the word 'cat' is a symbol of a cat and the name McFluffyPants is an index of (this particular) cat", and that makes sense. And I keep in mind that (written) words are great examples of quite purely symbolic things. Then I read a linguistics book and they discuss how pretty much all words are arbitrary (and thus symbols) but then you say "that cat over there" and suddenly the word "that" is also an index. This also makes sense since "that" really is pointing something verbally, and there is even a fancy term, deixis, for this process. Makes sense too. Then you read Scollon & Wong Scollon on the basics of geosemiotics, and I learn that an index is anything that points to something else, physically or abstractly. And in that context that makes great sense as well!

I happily input to my brain these three internally coherent approaches, but the internal mathematical machinery I have in my brain starts to integrate these all and throws a hissy fit. So part of the problem is obviously just that I am trying to push a square peg to a triangular hole. My mind is being a 'bit' rigid with the concept of a definition, and I'm not moving fluidly between the various concepts that are being meant.

Nevertheless, my brain does what it does, and after some thinking it suggests to me that "index is anything is based on pointing to something, no matter if literally, abstractly or via causal means". I congratulate myself on the insight, but after a while realize that this covers all possible signs. Isn't iconicity just pointing through resemblance and symbolicity just pointing through social convention? Let's raise this as Sub-problem 4: Is everything an index?

Note that my issue here is different from what e.g. Scollon & Wong Scollon state as a natural thing; essentially all signs we meet have an indexical component. My reading of Scollon & Wong Scollon is that their purpose is to point out that all of the signs we see are strongly tied to the sociocultural context and linguistic landscape where they appear. Furthermore the act of placing a sign to the world takes part in forming how the sign will be interpreted, thus making pretty much anything that is situated in the world an index in part. This, to me, is a very valid point. My problem is more on the definitional side of index, as in e.g. "how to separate the indexical properties from the symbolic properties of sign", which we'll look at next.

Sub-problem 5: What's the boundary between a symbol and an index?

So. If a typical property of an index is that "it signals things by pointing at them in some fashion" and that "its meaning depends strongly on the context", then isn't symbol just an extreme version of an index? Especially since we have in the idea of 'linguistical index' that has removed the requirement of spatial closeness or causal connection to allow e.g. deictic terms to work as indexes? If neither an index nor a symbol need to resemble⁵ the thing they point at but only derive their meaning from cultural context and agreement, then what's the difference? You might argue that the meaning of an index changes in different contexts, but so does the meaning of symbols in different cultures; e.g. the swastika carries very different meaning e.g. in classical Hinduism or in European politics.

In my eyes the difference is that of a scale. Symbols tend to be more universal and permanent, whereas indexes can vary within the same people and culture from moment to moment. The extremal examples for me would be something like:

• Pointing with a finger can change very rapidly; it takes me less than a second to change which berry I point to. So at least with the background agreement of what pointing means in general, the actualization of the pointing changes very rapidly.
• Personal pronouns like "you" can change their meaning even within a single spoken sentence, especially when accompanied by pointing: "You, you and you are now volunteers!" So this would be an index in the sense of linguistics.
  • Likewise temporal adverbs like "now" will change their meaning almost constantly by nature.
• A sign saying "KEEP OUT!" will usually have different meaning depending on if the viewer is an outsider or part of the in-group that wishes to keep outsiders away with a sign. This would again thus be a quite straightforward case of indexing in the sense of Scollon & Wong-Scollon.
  • Besides the indexing of the difference between the in-group and out-group, the text would also index the linguistical landscape being written in english, meaning that it should be only expected to work in a setting where any reader is expected to understand english.
• The "OK-gesture" created by forming a ring with your thumb and index finger while keeping the other fingers extended (👌) has different meanings in different cultures. E.g. in english-speaking countries it usually means "okay", while in Brazil it is a very rude gesture similar to flipping someone off. Here we feel that we are moving a bit more to the gray area between symbols and indexes. I wouldn't push too hard to classify this sign as either an index or a symbol too strongly without the context in which it is discussed.⁶
• We don't quite have the hutzpah to claim that some symbols would be universal across all human cultures, but we would still suggest that a human skull might work as a good candidate as a universal symbol of death. Of course, most skull-symbols we see are actually icons of a human skull, but the human skull itself would then be symbolizing death. (Well, an actual human skull would be an causal index of the particular death of the skull's original inhabitant, but a symbol of the generic concept of death or of your personal death.) In any case, from the point of view of universal usage⁷ I would set the human skull as the extremal example of a symbol and not of an index.

What does the old master say?

So, when you have problems understanding a concept, the age old advice is that you should read the old masters. Charles Sanders Peirce was not only a philosopher and one of the founders of semiotics, but also a mathematician. So maybe we can skim some insights suitable for a mathematician's mind.[^8] We've listed below some (but not all) of his many quotes about the definition of icons, indeces and symbols - though he was a mathematician these parts are not mathematical definitions, and he defines the terms in different words in different works as he discusses the idea of signs in different contexts. We've used the (apparantly standard) way of citing Peirce by his collected works, where e.g. "CP X.zzz" means page zzz from the volume X of "the collected works of Charles Sanders Peirce".

Various quotes

The following quotes are all from the collected works of Peirce, any emphasis or boldening of text is done by me.

Firt we find the following:

[...] it has been found that there are three kinds of signs which are all indispensable in all reasoning; the first is the diagrammatic sign or icon, which exhibits a similarity or analogy to the subject of discourse; the second is the index, which like a pronoun demonstrative or relative, forces the attention to the particular object intended without describing it; the third [or symbol] is the general name or description which signifies its object by means of an association of ideas or habitual connection between the name and the character signified.

Peirce, CP 1.369

So here Peirce is also discussing also linguistical concepts like deictic terms, and is not restricting the index to causal connections. Instead we get the description that an index "forces the attention to the particular object intended without describing it". This especially separates the index from the icon. Symbol is differentiated by describing it as a "general" concept, which Peirce elaborates about a lot in other work. In this approach we see that the key difference between the descriptions of an index and a symbol is that the index is "forcing the attention to". The whole semiotical theory of Peirce very much relies on the idea that there is always someone doing in the interpretation, but in this definition it is only in the index where we refer to the someone via talking about their attention. With the description of both the icon and the symbol, they in some sense "are" instead of "do", unlike the index which is forcing the attention of someone. So in here we would feel that even though both icons and especially symbols are dependent on sociocultural agreements, the index is really dependent on what is happening in the here and now. In particular, as it is forcing the attention to something, we again see the idea of the index pointing at something in the 'immediate vincinity'.

Then we have another version:

There may be a mere relation of reason between the sign and the thing signified; in that case the sign is an icon. Or there may be a direct physical connection; in that case, the sign is an index. Or there may be a relation which consists in the fact that the mind associates the sign with its object; in that case the sign is a name [or symbol].

Peirce, CP 1.372

Here we are clearly working in a different context since we limit index to direct physical connection. We are not going to start expanding on the different contexts of this quote and the previous one because even though we like the writing of Peirce, it doesn't make us happy and the collected works have about 5 thousand pages of it. But we feel it important to note that Peirce has also used this "physical connection" definition.

Then we have the following, much more verbose approach:

Sign degenerate in the lesser degree, is an Obsistent Sign, or Index, which is a Sign whose significance of its Object is due to its having a genuine Relation to that Object, irrespective of the Interpretant. Such, for example, is the exclamation "Hi!" as indicative of present danger, or a rap at the door as indicative of a visitor. A Sign degenerate in the greater degree is an Originalian Sign, or Icon, which is a Sign whose significant virtue is due simply to its Quality. Such, for example, are imaginations of how I would act under certain circumstances, as showing me how another man would be likely to act. We say that the portrait of a person we have not seen is convincing. So far as, on the ground merely of what I see in it, I am led to form an idea of the person it represents, it is an Icon. But, in fact, it is not a pure Icon, because I am greatly influenced by knowing that it is an effect, through the artist, caused by the original's appearance, and is thus in a genuine Obsistent relation to that original. Besides, I know that portraits have but the slightest resemblance to their originals, except in certain conventional respects, and after a conventional scale of values, etc. A Genuine Sign is a Transuasional Sign, or Symbol, which is a sign which owes its significant virtue to a character which can only be realized by the aid of its Interpretant. Any utterance of speech is an example. If the sounds were originally in part iconic, in part indexical, those characters have long since lost their importance. The words only stand for the objects they do, and signify the qualities they do, because they will determine, in the mind of the auditor, corresponding signs.

Peirce, CP 2.92

So here we get to read again very different approaches. Note that in the descriptions here, symbol is "a Genuine Sign" since it depends fully on the Interpretant, the index is "a degenerate sign in a lesser degree" since it has a relation to the object that exists independently of the Interpretant, and the icon is "a degenerate sign of greater degree" because it carries its meaning by "merely of what is in it" with no relation to outside world. So far I haven't really understood the example of an icon that Peirce gives as imaginations of acting. But we do see here that the Symbol is mentioned as special that the definition is quite straightforward. As per the difference in the definitions, note that even though an Interpretant will form a relation between an icon and the object it represents, this relation is really created by the Interpretant based on the resemblance of the icon to the object. This contrasts both the index where the relation exists without the Interpretant, and the symbol where the sign carries no resemblance to the object and thus the relation is formed independently from the content of the sign. Recall from the first quote we showed that an index "forces the attention to", meaning that the Interpretant has no agency in selecting where the attention is focused - the relation is there regardless of them.

Note also that here we see the mention that all words are symbols, and can only get their meaning through their "Interpretant" i.e. the somebody who is reading the word and forming its meaning. On the other hand, in the very same quote we see it mentioned that the exclamation "Hi!" is an index of present danger. So again; these are not differentiating concepts.

Next we have yet another approach.

If the Sign be an Icon, a scholastic might say that the "species" of the Object emanating from it found its matter in the Icon. If the Sign be an Index, we may think of it as a fragment torn away from the Object, the two in their Existence being one whole or a part of such whole. If the Sign is a Symbol, we may think of it as embodying the "ratio," or reason, of the Object that has emanated from it. These, of course, are mere figures of speech; but that does not render them useless.

Peirce, CP 2.230

Without the actual context, the choices of words might seem a bit peculiar, but nevertheless we start to get a feeling of a theme here. We again see the index and the object being related by being part of the same thing or pair, whereas for the definitions of icon and symbol here I am not gonna touch without some more context. Luckily they are merely figures of speech according to Peirce.

Finally we get three separate quotes, each defining one of the three types.

An Icon is a sign which refers to the Object that it denotes merely by virtue of characters of its own, and which it possesses, just the same, whether any such Object actually exists or not. [...] Anything whatever, be it quality, existent individual, or law, is an Icon of anything, in so far as it is like that thing and used as a sign of it.

Peirce, CP 2.247

So here the last sentence is especially interesting for us. It both again defines iconicity as likeness, but also requires that a likeness needs to be used as a sign of a thing before it turns into an icon. We find this an interesting thought, especially with the start of the quote where Peirce says that a sign can be an icon even if the object it refers to doesn't exist. At minimum what we get from here is that in this context Peirce doesn't allow literally everything to be an icon of itself by default.

An Index is a sign which refers to the Object that it denotes by virtue of being really affected by that Object. It cannot, therefore, be a Qualisign, because qualities are whatever they are independently of anything else. In so far as the Index is affected by the Object, it necessarily has some Quality in common with the Object, and it is in respect to these that it refers to the Object. It does, therefore, involve a sort of Icon, although an Icon of a peculiar kind; and it is not the mere resemblance of its Object, even in these respects which makes it a sign, but it is the actual modification of it by the Object.

Peirce, CP 2.248

We're not gonna dive into the terminology of qualisigns, legisigns, sinisigns and the like. But what we again see here is the requirement that an index has some true Interpretant-independent connection to the object. Furthermore note that Peirce here says that in this approach the index always has some iconicity built in to it as well as it shares some quality (or likeness) with the object since they are "really affected".

A Symbol is a sign which refers to the Object that it denotes by virtue of a law, usually an association of general ideas, which operates to cause the Symbol to be interpreted as referring to that Object. It is thus itself a general type or law, that is, is a Legisign. As such it acts through a Replica. Not only is it general itself, but the Object to which it refers is of a general nature. Now that which is general has its being in the instances which it will determine. There must, therefore, be existent instances of what the Symbol denotes, although we must here understand by "existent," existent in the possibly imaginary universe to which the Symbol refers. The Symbol will indirectly, through the association or other law, be affected by those instances; and thus the Symbol will involve a sort of Index, although an Index of a peculiar kind. It will not, however, be by any means true that the slight effect upon the Symbol of those instances accounts for the significant character of the Symbol.

Peirce, CP 2.249

Again, we get that symbols are defined by general laws rather than any "real affection". Note however, that here Peirce describes how any symbol has built in to it some indexicality. To our reading the argument is based on the idea that a symbol like the word "tree" refers to all trees, real or imaginary, and this collection of "all possible things that a 'tree' could refer to" is then connected to the word "tree". This connection happens regardless of a particular Interpretant, so the connection creates indexicality. I think.

Afterthoughts on quotes

So, reading Peirce does feel like reading the work of great mathematicians after trying to work out something yourself. They have clearly thought about the same topics than you have, though even their questions were better and they had full theories as replies. Some of which you even partly understand.

As said, reading Peirce doesn't make me happy, like he intended, but it does contain an astounding amount of useful thought. I regret that I don't have enough time or patience to properly study the philosophical context in which Peirce writes to truly appreciate more of his work.

I still kind of hope that there would be some overaching concept that Peirce is showing different facets of, but such concept might not be very expressable. So perhaps the best way is just to show the facets.

Solutions?

So after listing the problems out loud and reading Peirce, I think I am arriving to a state of mind where the concept of an index fits to my head. Let's elaborate on what that state of mind is. I'll first discuss some general thoughts and then try to answer my sub-questions.

General answers

Everything is relative and context dependent. The sign is used by someone to communicate something to someone else⁸, and this context of communication and the context of the whole socio-geo-cultural-political-linguistic landscape will be a part of the sign interpreation process. This means that this is a massively complex thing and trying to tie the concepts down with a one-size-fits-all definition would probably not work very well. Instead of that, it is better to describe in different settings how you would approach the themes of iconicity, symbolicity or indexicity and then use that approach as your lens and tool in analyzing things.

In particular, I find that the terms icon-symbol-index always come as a triplet and their definitions are relative to each other and depend on the setting. The over-arching theme tends to be that, just like all the books say, an icon resembles, a symbol is conventional, and an index is pointing.

Answers to sub-problems

1. How does pointing work? It works exactly as you think it works. You point at something, and the shared context between you and the Interpretant who is watching you point means that they can infer what pointing means in general and if you are pointing at a berry or a board. The various possibilities that pointing might mean or how it might be deconstructed are not problems; instead they improve the expressive power.

2. How does this indexing really break down? It can break down in many ways, most of them completely valid in some context. Furthermore, Peirce already discusses a lot about the idea that in the triplet of a sign, interpretant and object, the sign usually creates a new sign within the mind of the interpretant. And that sign can create more signs in your head. You can use these recursive signages to study a situation better, and you don't have to try to figure out "the correct one" since they are all just tools or frames of reference.

3. Indeces at the literature. There is no real problem unless you're trying to find a mathematical definition. The general tool of semiotics needs to be fine-tuned differently in different subject areas, and the fine-tunings naturally don't match.

4. Is everything an index? Not in practice no. There are non-indexical meanings as well so the concept is not void of content. You can discuss about pointing and use it as a well-functioning tool in many different contexts without having to include everything underneath the umbrella of indexing. Though as Scollon & Wong Scollon point out, pretty much every sign you meet in the world has an indexicality as a part of it.

5. What's the boundary between a symbol and an index? Symbol relies completely on social agreement. Index relies on a generic framework of social agreement as does all communication, but it is meant to point to different things within those agreements. It is a pointing tool, not a fixed concept. Trying to find the exact boundary in edge cases is fun but counterproductive for semiotic analysis.

Concluding remarks?

This has been good for me. I'm not sure how useful other people will find this text where I describe a problem I had and how I solved it, or if it makes any reader happy, but at least my brain is not convulsing anymore.

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[^8] Peirce has, somewhat infamously, said that he did not write to make his reader happy. This is a familiar pathos from the writings of many mathematicians as well. Peirce did not fail in his task.