Buzz..
For some TV's that show closed captioning (especially older sets that do not have a separate section at the bottom of the screen), these 'snipes' also cover over some of the words. Or when a show adds words to the bottom of the screens when the people on the tv show aren't talking loud enough, those words also are covered over with the ad information. That IS a little annoying sometimes.
I see it on virtually all of the big 4 networks (NBC, CBS, ABC, and FOX) though prime time seems to be the worst time for it. Most of these ads seem to pop-up just as the show is returning from a commerical. Some are random throughout the shows. And most of what I see are ads for OTHER shows that the network is trying to push attendance up on.