Linguist Ferdinand de Saussure: two-part model of the sign:
Signifier -- spoken word, written word, flag, etc -- something that represents a concept.
Signified -- the concept that the signifer stands for.
For example: the word "cat" is the signifier, and the concept of a cat is the signified.
The two together constitute a SIGN
For example: the word cat is the representamen, the concept cat is the interpretant, and the cat itself is the object.
Semioticians have mapped out networks of such sign systems. Roland Barthes, for example, wrote a book titled "the fashion system" about the semiotics of clothing in Euro-american popular culture -- why brides wear white and mourners wear black for example.
There are several conceptions of the word "symbol". From the basic
sense of the word-that of "a sign representing something
else"-interpretations vary. Symbols are thus today distinguished from
other signs by not being translatable into one, unambiguous meaning. Paul
Ricoeur talks about symbols as being elements with "surplus of meaning" (Ricoeur
1976). While this is true today, it may not always have been true. We
simplify by suggesting that symbols resist reduction in the way that icons
are most effective because reducible. Somehow established by convention,
symbols are then imbued with diffuse and unclear associations and meaning.
(Lisbeth Bredholt Christensen & David A. Warburton; Aarhus Universitet,
On semiotics of popular culture see http://courses.wcupa.edu/fletcher/solomon.htm
For more on semiotic theory see "semiotics for beginners" by Daniel Chandler: http://www.aber.ac.uk/media/Documents/S4B/semiotic.html