What kind of communications systems are there in general?

Natural and artificial communications systems are commonly distinguished. A natural communications system is one that arises spontaneously from human (or other animal) interactions, such as a natural verbal language or a nonverbal sign language. Artificial communications systems are ones deliberately invented, usually to serve specific functions, such as the international conventions for signs and notices, the signalling of sports referees, etc.

Signs in a Natural System
Signs in an Artificial System