The concept of indexicality is a wide ranging one, but many facets of this phenomenon are recognizable to non-specialists. One facet is the way that certain kinds of language are understood to point to (or be indexical of) certain kinds of people. Today’s media on indexicality comes from Friends.
The way we use language inevitably gets read to mean that we are a certain kind of person: cool, or old, or like a scientist, or like a Canadian, or like doge, whatever. There’s no one iron-clad set of rules that could tell you how to sound a certain way: these linkages between talk and person are always embedded in social interaction and are subject to change.
This entry from the show Friends has Joey trying to take advantage of the indexical qualities of some words to make himself sound smart. Because of some very poor guidance from Ross, Joey ultimately fails to get his letter understood as the kind of thing a smart person would write. Unfortunately, poor misled Joey remains the target of the humor here, rather than the ideologies that evaluate language use in order to enforce social hierarchies.
Speech Events 
Nice example. This makes me wonder what might index intelligence in languages which (unlike analytic, isolating English) tend towards long words in general (e.g. (poly)synthetic, agglutinating languages). Is word length a universal marker of difficulty/ user prestige? What other features index intelligence (or similar desirable attribute) in other languages?
Hmmm, I imagine it may frequently be the case but I think intelligence is so frequently wrapped up in something else (like what kind of intelligent person are we talking about? A priest? A political leader?) that word origin as opposed to length might be a better indicator. Obviously French or Latin here in the West but in West Africa for instance, entire registers indexing intelligence include not just transparently borrowed sentences/expressions but also vocabulary sets that originally stem from Arabic or Soninké in ways that are frequently transparent to a linguist but not the users themselves.
That is a cool question. I suspect that anything could, but I don’t think I’ve ever read much about indexing intelligence. And there’s always going to traps along the way. Actually now that I think about it, maybe I read something about how somewhere the lower class speakers talk like the upper class speakers did 20 years ago, always chasing the speech patterns that were supposed to be prestigious and refined, only to have the people with economic power change the game. That’s a different case that what Baby Kangaroo is striving for, though.
[…] *** discussing what kinds of meaning and how it attaches to certain kinds of people is certainly a discussion for another time. See indexicality. […]
[…] with certain kinds of people. This association is the phenomenon Joey tried to exploit in the Media Dictionary entry for indexicality. Registers are models of those associations between bits of communication and […]