the smell of pizza is not pizza-in-itselfNow lets throw some definitions up on the board (courtesy of cedarseed.com):
Sign: Signs are events or things that direct attention or are indicative of other events or things.These are fairly close in meaning, but I'm sure as hell nobody taught me to love the smell of pizza. So it's official: pizza smell is a sign, which points to pizza. Please feel free to comment with supporting/debunking evidence.
Symbol: A symbol represents something in a completely arbitrary relationship. The connection between signifier and signified depends entirely on the observer, or more exactly, what the observer was taught.
Just so you don't think I'm taking credit for anything.