Sign, Symbol, Icon

Symbols - A symbol has no logical meaning between it and the object, a homepage icon which is a house for example. Other off screen symbols which may help explain the difference are flags. Flags are symbols which represent countries or organizations. Again, the crossover to design and branding is very evident in these signs.

Index - An Index signs is a sign where there is a direct link between the sign and the object. The majority of traffic signs are Index signs as they represent information which relates to a location (eg, a 'slippery road surface' sign placed on a road which is prone to flooding)

Icon - An Icon sign is a sign that resembles something, such as photographs of people. An icon can also be illustrative or diagrammatic, for example a 'no-smoking' sign.