Actually up here in Toronto I haven't had an issue in a year and a half - nobody has touched the thing when I park it outside of work and I generally rely on the steering lock (and the lack of knowledge about mopeds... a targa looks heavier than it is) to keep it secure. But some areas and some cities you do that it'll be thrashed or gone faster than you can blink. Overnight, I always park it indoors in a secure spot... but I have no qualms here about leaving it out while going out or going to work (but it is also pretty downtown... and at all hours there tend to be people going by)
A good lock is still a good idea however - keep someone from casually picking it up and tossing it into a pickup so they can take off the steering lock at their leisure. Or just strip it for parts.
Not going quite as far as Ree does (but in his area I bet he has to) you might also get something like a notebook lock/alarm... something that senses movement and goes off... might at least scare off the casual kid trying to get something for a joyride and most of them will not cost much. :)
(Why do I suspect anyone trying to pick Ree's pocket would end up losing a few fingers at that ;)