In the US, those are radio stations WWVB for clocks and watches, and WWV/WWVH for shortwave.

One thing I think is interesting is that not only are the digital formats these carry synced to an atomic clock, but the radio carrier wave is too. So if you need a very precise 10 MHz signal in the lab, you can hook up a shortwave antenna and a filter, and receive the precisely-on-frequency signal broadcast from WWV.