A friend of mine and fellow grad student in the Tufts Psychology Department (Mike Slepian) recently had a paper come out that's been getting some press lately. Interestingly enough, it relates to the common cartoony emblem of the lightbulb above the head. This symbol is a conventional sign for "inspiration" in comics and cartoons, so the authors wanted to see if real lightbulbs could actually give people inspiration.
Lo and behold — they did! In a series of experiments, participants were asked to do logic problems and near them light was turned on from either a lightbulb or an ambient overhead light. Participants with a lightbulb consistently completed more logic problems correctly than those with the overhead light.
This indicates that, not only do the conventional signs of a lightbulb represent inspiration, but that meaning has become entrenched enough that it actually feeds back on performance in cognitive tasks. That is, the graphic symbolism has affected the way we think and behave.
The idea that language effects thought and behavior is called "linguistic relativity" or Whorfianism and is a highly contentious debate. The vocabulary of visual language may have some degree of linguistic relativity as well — at least for this particular sign. I'd love to see more research like this with other graphic signs. I'm not sure what my prediction would be, but it'd certainly be interesting...
Slepian, M.L., Weisbuch, M., Rutchick, A.M., Newman, L.S., & Ambady, N. (2010). Shedding light on insight: Priming bright ideas. Journal of Experimental Social Psychology, 46, 696-700.