The last part of the definition describes communication as being done “through a common system of signs, symbols, and behavior”. A common system enables successful transmission of ideas within, between, or among communicators. And these ideas may come in different forms. A sign is an indicator or marker for something very specific, very concrete, and in general, unambiguous in meaning. For example, road markers are called signs because they usually convey something very specific like STOP, a street name, or a certain speed limit.