Helmets can safely be left on the bike, because used helmets have no resale value.
I have left my helmet unattended for 8-10 hours a day in downtown Portland for four years, no thefts, even with fancy helmets.
I have left my helmet unattended for 8-10 hours a day in downtown Portland for four years, no thefts, even with fancy helmets.
Anecdotally, in the DC area people lock their helmets to their bikes all the time. I've had one bike stolen here but never a helmet. In fact when they stole my bike, they left the helmet that was locked up with it.