It's a focusing lens that I had laying around and it fit right in the tip of the laser pen. You can use pretty much any acrylic or transparent material that will fit in that hole to disperse the light. Hell ,you can even use office magic tape to disperse the light, just tape one layer over the hole. It even works with my 2000mW lazer when I want to convert it into a UV flashlight.
Now I assume we are all adults and I don't have to warn you about the dangers of playing with lazers, just in case somebody has the idea of getting one of those high-powered 2000mW lasers and gets the beam reflected back into his unprotected eyes. Stick with a safe 5mW , higher than that and you might also burn your nice black watch dial.
Another WIS thing that I do is choosing my watch first and then the wardrobe to match my watch, I also choose the watch I will be wearing in the evening rather than first thing in the morning.