Do unset clocks flash 12:00 in locations that use 24-hour clocks, or do they flash 00:00?

I can't honestly say I ever paid attention, but I just checked all clocks I could find, one flashes 00:00 and the other 0:00. Most if not all clocks I've used had a 12 or 24-hour mode, not sure what happens if you set to 12-hour and unplug it (probably just reset to defaults).