1. A method of identifying a signal received by an audience member's television receiver for determining audience ratings comprising the steps of: detecting the occurence of a first event in the functional operations of he audience namber's televison receiver; detecting the occurence of a second event after the detected first event in the signal to be identified; extracting a signature from a single frame of the video signal to be identified after the occurrence of the second event; storing the signature and the time of occurence thereof; and comparing the stored signature with reference signatures that occurred at approximately the same time as the stored signature.