On some watches you may see the

On some watches you may see the lettering “T Swiss Made T” across the bottom of the dial. This lettering means that it is a Swiss watch and that it contains a certain amount of Tritium.

In order for the time to be read in the dark a substance that glows
in the dark is applied to the hands and markers on the dial.

The most popular substance used is Tritium.
Tritium emits a very low value of radiation that is contained within the watchcase. It is of no threat whatsoever to the health of the person wearing the watch.