I've been wanting to make labels for my sanwu lasers using @Trevor 's excellent laser label generator. It's quick & easy, costs almost nothing, and should be strong enough to last for a while.
First, print the label. I printed it just shy of 2 inches long, large enough to be noticeable.
Fold it exactly in half, then trim the excess white if you want it to look neat.
Loop a piece of string and tie a knot at the end. Tape it to the inside of the label, them trim the excess tape. maybe put a tiny bit of superglue for extra strength?
Fold the label, then tape the whole thing around the opening of the label. Trim the excess tape.
Attach the label to your laser.
Done, now it looks dangerous!