"Skills, rules, and knowledge; signals, signs, and symbols, and other distinctions in human performance models" #readingToday
To sum up, the three levels of behavior in the present context are characterized by different uses of the information available, and the distinction is very clear from an information processing point of view. Signals are sensory data representing time-space variables from a dynamical spatial configuration in the environment, and they can be processed by the organism as continuous variables. Signs indicate a state in the environment with reference to certain conventions for acts. Signs are related to certain features in the environment and the connected conditions for action. Signs cannot be processed directly, they serve to activate stored patterns of behavior. Symbols represent other information, variables, relations, and properties and can be formally processed. Symbols are abstract constructs related to and defined by a formal structure of relations and processes-which by conventions can be related to features of the external world.