All signals, with the exception of very special ones such as human verbal communication, evolve to be reliable. Communication systems that have been considered as systems of conventional signalling are reinterpreted as reliable systems by indicating the investment which increases their reliability. Examples are given from decorative patterns and set specific signals, such as status signals. The general importance of reliability is further discussed for cases such as the chemical signals within the multicellular organism, in which there is no conflict between the communicating parties. The reliability of signals which display symmetry, as is measured by the `fluctuating asymmetry', is interpreted as a consequence of the investment required of signals that coordinate development.