In this way, symbols transform themselves into specific ideas or conventions from the world of ideas and language and these symbols can often change according to society and historical period. Signs therefore signify through the use of code. Sometimes, the sign is obvious. Other times, it has to be decoded.

Icons and Symbols

Two primary codes are Iconic and Symbolic. Icons are a literal representation of the object (the referent) - e.g. A painting of a hamburger is meant to represent the original. Symbols, on the other hand, are meant to allude to something such as Turner's sunset, or a traffic sign, flag, or word that points to a meaning behind that. Some representations such as a Coke can be both -- it is both icon and representation of American consumption.

Words are a typical symbol. By itself they mean nothing. The word (or symbol) 'rat' can mean different things in different countries. It is composed of syllables which turned around can mean something else to the one who is privy to that information.

We also have a representation known as indexical code which is a symbol that points to the existence of something that may not be evident such as smoke pointing to the possibility of someone else being in the neighbourhood. Indexical signs also indicate a causal connection between things such as footprints that automatically tell us that someone else has recently...

auction house, 2008 produced by the English artist Glen Baxter. The painting itself is iconic. It shows cowboys standing outside an auction house looking at a large painting hung on the wall. The hung painting is totally black. It is produced by the Russian painter Malevich and is known as Malevich's Black Square. Although, all we have is representation of things that we see in real life, each of these referents is also symbols or signs to concealed meaning. The painting alludes to the age of the 1950s, the period of Cold War between America and Russia. Baxter's painting proposes a humorous and ironic connection between American and Russian avant-garde art (by having the cowboys contemplate Malevich's painting.) We are also given the contrast (again this is a symbol) between the action-known cowboy and the stereotypical passive artist. Contrast is infused through symbol the whole appearing through the icon. Yet, each of these representations or symbols may be false since not all cowboys are active nor are all artists passive.
It is in this way that contemporary visual cultural with its convoy of signage has an influence on us that is beyond our perception.

Source

Reading Visual Culture. Lecture 2: Visual Culture and Representation (PPT)