Semiotics

Semiotics is the science of signs. The founder of semiotics (or the interpretation of signs) was a Swiss linguist named Ferdinand de Saussure. He said that signs are made up of sounds and images, and what concepts these sounds and images bring to mind , he called this the Signified.

American philosopher Charles Sanders Peirce is the founder of semiotics (.The trichotomy of icons, indexes, and symbols):

Icon: A literal sign. Its a sign that physically resembles the thing it stands for.

Index: A Implied sign. Its a sign that implies something.

Symbol: A learned sign. It is something we learn what it means.

An example of these:

Icon: A picture of a dog.

Index: A paw print.

Symbol: The word 'Dog'.