Semiotics is the study of signs:

An Iconic sign is something that looks like its object. For example in my work, the book, statue and Elvis Presley are all iconic signs

An indexical sign is a sign that has a link to its object. For example in my work, the newspaper, television and record all have links to media

A symbolic sign is something that has a random link to its object. For example in my work, the blue font, the black and white background and the fire are all symbolic signs.