Bicycle, not motorcycle, but still gives that same sense of satisfaction. Great advice in the comments too.. I need to go take a photo of the serial number on my bicycle! My other (older bike that I don't care as much about) disappeared from a UBC bike rack this summer too, which makes me more wary.
When I was in China, I also accosted a thief. I saw him take my friend's cellphone from his bag. I yelled so loud, probably everyone on the block heard, grabbed the man's arm so he couldn't run, took the phone from his other hand and gave it back to my friend. I think the thief was so surprised, he kind of just complied and nodded apologetically. So ya'll know if I go biking with you, you'll be safe with me because my bodyguard skills are tried and tested, and I'll chase any thief who tries to take off with your bike