It used to be Ra (Radium), yes I would think so, it is luminescent in the dark, glowing without sun-light or other source of energy with a half-time of 1200 years, thank you Marie Curie!
Actually it is not Ra (Radium) or H-3 (Tritium) since they’re radioactive and unless you have a really old watch it is most likely a Strontium Aluminate or LumiNova that makes it glow in the dark. My watch is very new…
I did not know that until just now. Nor did I know the history behind the 21 gun salute until today… another story altogether. Interesting facts.