Around these parts, it's not that bad of an issue. I wouldn't leave my helmet locked on my bike overnight and try to not leave my bike parked in a shady part of town for very long, but I don't really have a fear of leaving it for several hours. When I'm running errands, etc. I typically leave my lid hanging on the right grip, with my gloves tucked into the helmet...haven't had any issues. I'm sure it will happen at some point, but so far (20+ yrs so far) I haven't had anyone mess with my bike/gear.
When I take a longer trip to unknown areas, I tend to be way more cautious and lock up my bike (front rotor lock) and carry my stuff with me.
When I take a longer trip to unknown areas, I tend to be way more cautious and lock up my bike (front rotor lock) and carry my stuff with me.