Personally, I never leave my helmet or any other gear when I leave my bike parked in a public area. I've noticed recently, probably more so now then ever before, it seems to happen quite frequently. I parked my bike out the front of a large shopping centre and went inside (with all my gear - helmet included). I was in a shop that overlooked my bike and noticed another guy on a bike pull up right next to mine. He got off and left his helmet and jacket attached to the bike and walked in side. As I walked out I had a look at his bike and noticed that the helmet and jacket weren't secured to the bike in anyway - I could have picked it up and walked off and no one would have noticed any different. Have you ever had your gear stolen as a result of leaving it with the bike?