Those are Kuryakyn large silver bullets with shortened posts. With a half helmet on the lock, the helmet just covers the rear turn signal, and I don't get any scratches on the fender or anything else marked up on the bike. A full helmet can be a bit fidgety to get it on the lock, but it'll work.
I suppose if some idjit came along and whacked the helmet with his knee it could damage the turn signal, but I haven't had that problem in the 2 years I've had it on the bike.
