Semiotics

Semiotics study the linguistics in signs and non-linguistic sign systems such as, the use of colour and symbols.  The word was invented by the linguist and philosopher Saussure.  sassure was a swiss linguist and semiotician.  Semiotics is very closely related to the field of linguistics, which studies the structure and meaning of language more specifically.  Semiotics is usually found divided into three main branches:
Semantics: Relation between signs and the things to which they refer their meaning. 
Syntactics: Relations among signs often in formal structures
Pragmatics: Relation between signs and sign-using agents

In this example we have come to globally recognise the Mcdonalds logo and instantly know what it means.  The "M" has become a mental concept for what has become a memorised symbol.  The caption "I'm lovin' it" implies enjoyment when you receive this product.  It makes us believe that we will enjoy it (love it) and therefore buy it at the next opportunity.  The colours used are now also recognised.  The use of yellow is clever as it is the colour in which can be seen the clearest at the furthest distance.  Again putting in peoples mind that this product is always there - for our consumption.