Two stories about nifty broadcast tv hacks. The first is from Chicago tv in the 1980s, where a guy dressed as Max Headroom interrupted a news show and a Doctor Who repeat. Damn Interesting has a story, and YouTube offers a couple of clips: the Who hack itself, and Dan Rather's news story about it.
The second and more interesting one claims to have transpired in Wyoming, where this odd clip supposedly appeared on local tv:
I can't find any confirmation of it, though, so it could be a hoax of a prank.
...A hacker managed to ... all » interrupt broadcasts from a local programming channel (believed to serve several smaller communities in the county of Niobrara) and aired his/her own video. The video contained numerous clips of disembodied, human heads showing various emotions and "poses". The camera position changed often (usually every ten-to-fifteen seconds) and the video was often interrupted by a "SPECIAL PRESENTATION" announcement. This clip is taken from one of these intervals. ...
If it's not true, even better - a hoax about a prank. The ARG antecedent tradition lives on. The clip itself is odd, consistly mostly of chunky, retro titles. I can't tell if the whole effect is creepy or soothing.