Icons – These are signifiers that have some sort of physical resemblance to the things that they signify. Photographs and illustrations both (mostly) fall into this category, as they both have a resemblance to the things that are in the photographs. Spoken words that are onomatopoeias, i.e words that sound the same as the natural world, “bang” “whoosh” etc.
Symbols – These are signs where the signifiers are learnt. They are cultural symbols that have no natural resemblance. Most spoken language falls into the category as they are cultural conventions, and we learnt them at some point in our lives to understand them in context.
Indexes – Indexical signs are ones where the signifier can only exist because the physical presence of the signified. These may include smells, animal or music sounds, fingerprints and footprints. Almost all the clues in a detective story would all be indexical signs.
Mixing up the signs
confusion happens because some of these signs can fall into one or more category
For example, A “sign” on a toilet door that is the image of a stick man to show that this is the gentlemen’s washroom. The “sign” may be iconic because the man on the door has a physical resemblance to the signified, but is also a symbol because we have learn that this picture represents where men can use the loo.