Semiotics

Semiotics is the study of signs and its is proposed by Charles Sanders Pierce. Pierce's idea distinguish between three type of signs which are, "Icon" , "Index" , "Symbol".

Icon is something that looks like what it is representing. For example, what can you see in this sign? Yes, it is a fire exit sign that's because it is well known already. But, just looking at this sign, it could be some one running away from something, it could be a race, an exit of something, an outdoor running field or something.

When something else is added to the picture, the whole meaning changes and its completely different. The sign at the left changes the meaning of the picture, giving more information to this sign. The fire that represents fire is telling you that the person is running away from the fire.

But since the "fire" icon could represent something else maybe sound noise or some other stuff you could think of. So, the letter "Fire Exit" made the whole picture make sense and is telling what it is meant to tell.

Index is referred to their objects of any similarity relation. There is a cause link between the sign and object. In this category smoke is an index of fire, as smoke is caused by fire. In the picture below you can see smoke and you will automatically linked it to "fire".

Symbol is an arbitrary sign in which the signifier has neither a direct (iconic) nor an indexical relationship to the signified, but rather represent it through convention. They usually have no logical connection. 

Signs are dependent on contexts, ideas can be directly brought into mind without being directly experience. Meanings can be expressed in various ways through a variety of sign system music, gestures, pictures etc.

Bibliography:

http://www.youtube.com/watch?v=rEgxTKUP_WI