Not sure about TV, but radio shenannagins have been done, and not just the Soviets. I was once fiddling with my AM radio (I'm in Central CA) and picked up a nice AM station from Boise that played 70s and 80s rock one night. Right in the middle of "Walk Like an Egyptian" came a very powerful signal, clear as a bell, and the speaker ID'd the station as Radio Havana! And they were "spreading the truth about Cuba to the American people". I called the FCC the next day and they told me that it did happen from time to time, and not much could be done about it. This was back in the summer of '92 IIRC.