A friend had a Greeves 350cc scrambler. He used to leave the keys in the ignition and was convinced one day he'd come out and find a thief lying next to the bike with a shattered shinbone.
The bike was a BEYOTCH to start. If ya didn't have the throttle, ignition advance and decompressor set just right it would throw ya over the bars.
I always park my C10 next to a newer, prettier bike.
Best anti-theft method there is.