Semiology

Semiology is the study of signs. It is derived from the greek word semion meaning sign and logos meaning structure, so it actually means the structure of the sign. The signifier plus the signified equals the sign. Semiology was founded by Ferdinand de Sassure. He is the man who came up with the concept of the signifier and the signified.
According to Sassure, the word is the signifier and the concept is the signified. The two have an arbitrary relationship. You need the signified in order to understand the signifier, and vice versa. For example, if I were to say the word tree, depending on where you may come from, the tree that you are thinking of could be an evergreen whereas I could be thinking of an oak tree. The word oak would make it more specific but the concept is still the same. You understand the concept of tree when given the word. Semiology gets you to think about signs and words in relation to one another. The sign is unique because it encompasses the signifier and the signified.
Today you can't go too long without being bombarded by advertisements of some kind. Often times we take for granted the meaning of things that are being presented to us. Through uses of rhetorical devices, there are many ways in which we can convey more than one meaning with a few simple words. Sarcasm is one of those devices we might use and it is understood that whoever is saying the words doesn't actually mean what they say but when can we afford to just take anything at face value?
Deception is apart of our everyday experience. If we were to take people's word for it all the time we would be buying from every salesman that approached our doors. We must learn to find the true meaning of the sign and discern what to take to from it and what to leave behind.