A system identifies which of first and second signal sources is supplying a program signal to a monitored receiver. The first and second signal sources and the monitored receiver are located in a household. The system extracts a reference program signature representative of an output of the monitored receiver and first and second source program signatures representative of an output of the first and second signal sources. The system identifies which of the first and second signal sources is a source of the program signal in response to the reference program signature and the first and second source program signatures.