Pierce Charles Sanders Pierce is one o f the founders of semiotics as a discipline. He distinguished three basic types of sign which are the icon, index, and symbol
Icon An Icon: bears a resemblance to its object Example of an icon is the M in the Gmail.
Index Index: is a sign with a direct existential connection with its object Example of an Index is for instance if you see large amount of smoke coming from far away, its is an indication that there is a fire burning somewhere.
Symbol Symbol: a sign whose connection with its object is a matter of convention, agreement, or rule. Words, images, and numbers can all be symbols.
Semiotics Is the study of signs and symbols. It is in many countries and integral part of advertising theory. It is used more in France and Eastern Europe than other countries. It is relate to writing and language. Some cultures use more symbols in advertising than do others.