I can't see how any device is going to differentiate between TV content and randomly placed commercials. If the commercials occurred at the exact same time every hour, it wouldn’t be a problem. I would guess that if there was an easy way to detect randomly placed commercial breaks, Tivo and other DVR’s would jump all over that. I can think of multiple ways that TV broadcasters could send across such commercial break signals, but that would be like shooting themselves in their foot.
To the best of my knowledge, there’s nothing used on TV broadcasts that can be equated to the old Mutual Radio “bee-doop” tones or the CBS Radio chirp. Years of radio board op-ing (15 years ago) has engrained those sounds in my memory.
-Mike Tomei