This image is an example of a Representation. It is a representation because it is an extemely accurate and concise model of what it represents. In other words, it is a photograph. A photo is such a good quality representation because it is as close to actually seeing an object in person as one can get. From this representation, one can clearly identify this object as a car, (and if you're a Chevy person, specifically a 1961 Impala). Representations leave no details to the imagination and are able to spawn abstractions by artists.

This image is an abstraction. While extremely accurate and easy to identify, this abstraction of the actual Coliseum in Rome is not necessarily a representation. Factors such as light and color are left out. Different aspects of the scene in which this was drawn may have been left out by the artist, thus making it an abstraction. Drawings such as this are much more accurate than a symbol, yet lack the reality of a represenation.

This "check engine" light is a symbol. It lacks the realistic detail of a representation or faithful duplication of an abstraction. Instead, it only utilizes the bare necessities of an engine's shape to signify that something may be amiss in your car's engine. One can distinguish an air cleaner and fan, but that is about it. For someone who has no idea of what an engine looks like, there are words (symbols themselves) that say "check engine". This symbol has a purpose, and is not used for asthetic pleasure but instead the conveyance of meaning.