There are actually other time signals around the world.

I had a Casio wave ceptor (one with analog hands which it doesn't look like they sell anymore; I should have kept it). Anyway, looking at a model that's currently available (WV-200R, but there are 2 other models available), its manual says it gets signals from "Germany (Mainflingen), England (Anthorn), United States (Fort Collins), [and] Japan."

I was curious so I looked those up:

Mainflingen DCF77 77.5 kHz

Anthorn 60 kHz

Fort Collins WWVB 60 kHz

Japan looks like they have Mount Otakayoda 40 kHz, and Mount Hagane 60 kHz.

There are also some other countries that have time broadcasts (e.g. France. Anywhere else?) but not that that watch uses.