Signals refer to the way in which the message is transmitted.  It is inversely related to the concept of noise , for when noise is converted into a mathematical value, the signal transmitted has the potential to be enhanced to overcome the noise (Beck et al., 2005).

Shannon and Weaver's Mathematical Theory of Communication

Claude Shannon and Warren Weaver were both physicists working in the Bell Telephone Laboratories during the 1940's.  Because there were so many errors with telecommunication in terms of distortion and inaccuracy, the men were interested in creating a mathematical model of communication in order to better understand the physical problems that could introduce noise into an exchange.  They believed that if a mathematical value could be assigned to noise in an interaction, then it could be determined how much the signal should be increased in order to overcome the noise.  As a result, Shannon and Weaver came up with a linear model of communication proving that communication is about the process of transmission and the reception of signals (Beck et al., 2005).