Signs are distinguished from each other by their difference. The knowledge of any term is dependent on knowledge of the system. The materially produced representation. The mental concept to which the signifier refers. Four- legged barking animal.
Signs are conventional.
They are sent by a sender who wishes to communicate and understandable only to those who understand what is coded in the sign. For instance, smoke in a forest may be nothing more than the indication of a fire, or it may be a sign from one lover to another that the way is clear. This doesn't mean that it cannot change, only that we cannot individually change it by an act of will. Dictionary meanings indicate the most common relationships between signifiers and signifieds in any particular period. Quite often, however, new signifieds alter the meaning of a sign.