Here in the U.S. most if not all stations transmit digital information in
the vertical or horizontal retrace area of the signal. I think I have seen
articles in Circuit Cellar about decoding this info. The information is the
date and time, the station call letters and even the name of the on air
program. This is stored much the same way as the Closed Captioning.

this signal is how the new 'smart' (in some marketing guys opinion) are able
to set the clock. No more flashing 12:00, how interesting.

Michael