My TV and my VCR both support this (i.e. displaying the station name and grabbing the time from one of the stations). The info they use for this (in both cases) is from the VideoText signal which is sent during the vertical page flip. Note that VideoText supports two clocks: One that is displayed in the top right and one that is not displayed. Plus there might be a VPS signal on some stations (I really wished all stations sent those), but the VPS signal has almost nothing to do with real clock time, it only denotes the different programs (if a movie gets sent delayed, the according VPS signal will also be delayed).
Anyway: I noticed (due to a station that doesn't actually conform to the videotext/teletext/toptext standards) that both my VCR and my TV actually grab both the station name and the time from the top line of the text (i.e. clock from upper right corner, station name from upper left. Thank god both of my units allow me to select the station they get the time from.

cu,
sven