Max Headroom signal hijackings
On November 22, 1987, two television stations based in Chicago, Illinois, were hijacked two hours apart from one another by unidentified perpetrators. Both hijackings briefly sent pirate broadcasts of an unidentified person wearing a Max Headroom mask and costume to thousands of homes in the Chicago metropolitan area.
Source: Wikipedia — Max Headroom signal hijackings (CC BY-SA 4.0)