A sign is anything that has meaning. There are three sorts of signs: icons, indicies and symbols. An Icons is a representation that brings something to mind because of its resemblance to that thing. Drawings, photographs and maps are icons because they resemble the things they represent. Indices are signs that point to something--as an index in a book points to the pages in a book where you can find a word or concept. Smoke is an indexical sign of fire because it has a natural relation to fire and points to the likelihood of fire. (as in: Where there is smoke there is fire.) Symbols are signs that stand for other things because of human convention. The word tree and the number 2 are symbols. All words and numbers are symbols, because they stand in place of something else for which they have neither a physical resemblance nor a natural connection. ICONS
Most people who have even heard of the word, icon, either think it has something to do with Russian religious art--or else, with the little pictures that are used as buttons on a computer screen. That's because the word, icon, means image. In the case of Russian religious art, icons are paintings (usually on wood) that represent a religious personage such as a saint. In the case of computer screens, an icon is a tiny picture that represents functions--such as opening a folder; cutting, copying or pasting; and printing.
Icons, then. stand for things because they resemble them. There are two sorts of icons: projections and likenesses. Icons that are projections resemble things because they have a point-for-point relationship to them. Icons that are likenesses resemble things with less precision. The key word for both sorts of icons is resemble--for icons are signs that resemble the things for which they stand..
Icons as Projections:
It is probably not much of a stretch to recognize how a photograph or a drawing of something might be a point-for-point projection....