i saw one guy with two on the crane stock and one on the side of the handguard, i understand that big ones look cool on a chest rig but ones on rifles look stupid
I've seen people stick them on chest rigs so they can be identified, but if it's on your gun, they cant see it... And no-one can answer why, unless they say "it's tacti-cool"
I know in some Mil-sim's over in the states you use a red one to signify being dead and it would be easilly seen if you're laying down with the gun on your chest. Probably was copied for looking Ally AF.