Semiotics

Semiotics is the study of signs classified as symbols, icons, index and how these signs make up the majority of human interaction and culture. Without semiotics we would be unable to communicate; image speaking to someone who is blind that doesn't speak the same language as you. When you take away the visual and linguistic references that we used to communicate then you are left with no communication. Advertising has to be very cognizant of these cultural semiotics because they determine how you message is received. As we move closer and closer to a global culture, advertisers have to be more careful about their message because the 'target audience' won't be the only one seeing it.
For example, this ad for Groupon might be funny to most of the American audiences but it is seen as greatly offensive to the Tibetan people.

The American public might see the human right violations in Tibet as some far-away rarely-talked-about issue but the Tibetans don't see it that way. Could you imagine if the ad was changed to some issue with more media coverage in America like: Boston, Katrina, Iraq, or Israel? Many Americans would be outraged by the nonchalance shown by the ad towards issues that hit so close to home.
Advertisers often use metaphors, play on words, and jokes that only make sense in a certain language as well. This is a form of semiotics. 

This ad for Modelo, a Mexican beer, says "Modelos y Futbol. Para que Mas!" or in English "Models and soccer. What more could you want?" The play on words is Modelos, which means in spanish: models, refering to the sexy ladies in the ad, and/or Modelos, the plural form of the brand of beer. Any audience that doesn't speak Spanish, wont get the joke. This is semiotics in advertising in a nut-shell.