Thought you had heard it all, right???
I was riding with a bud, stopped and locked the helmets on the bikes through the D-rings. Both Shoie RF-900's.
Luckilly, my head was bigger than the theifs, as the strap had been cut off low to the D-ring from my buddies bike. Simple enough to repair I guess.
Take it with you, or keep it in sight.
PS better yet... years ago ('86), I had just passed through the Lincoln tunnel and was sitting at the light to turn right onto 42nd street. Sport bike pulls up next to me, nice, new, rider with no helmet. Two guys jump out of the low boy box van in front of him, cold cock the rider, throw the bike in the box van, pull pistols out and wave them at everyone looking, and take off. Just another reason to wear your helmet.