I live in a city where bike theft is a major dilemma for the "carbon fiber super rocket" crowd, I also teach waves of new riders every weekend and am constantly pressed on this very topic. The fact is, sadly, there is little to nothing you can do to prevent the determined thief from snatching your bike. Even "secure" underground parking garages have become havens for bike theft (one more thing the condo crowd has to worry about). Take comfort in this fact, in 10 years of riding vintage british bikes, I've never had an incident more serious than the local pre-schoolers leaving muddy fingerprints on my freshly polished tanks and cases. Evidence gleaned from police stats show that the overwhelming majority of thefts (at least in Toronto) are routed through the black market, and over to Europe. The vast majority of the bikes that are stolen are of the supersport class (anything with an R or S on the end of it), as these seem to be far more prolific on NA roads than European roads. Your biggest worry would be the casual joyrider, in which case I'm not certain how many "youths" would have any idea what the hell a Norton is to begin with much less have the inclination to try and fire one up. When I leave them parked outside overnight, I find a simple non descript bike cover is usually all that's necessary to throw off the casual joyrider.