A computing system is programmed to detect if program content is presented on a channel. A program signature is determined based on set-top box tune data from set-top boxes in a market in which it is known the program content was presented. The program signature can be compared to program signatures from other local markets or from the same market to determine if the same program content was presented. In some embodiments, the program signature represents the number of set-top boxes simultaneously tuned to the channel on which the program content is presented.