On july 1, 1941 The few fans watching the Brooklyn Dodgers’ game on WNBT are witnesses to a breakthrough in marketing: for 10 seconds before the first pitch of the game, the screen shows the image of a clock superimposed over a map of the United States. A voice then states “America runs on Bulova time”. It is the first television advertisement ever broadcast in the United States.
Source
Baseball Reference July 1