Not in the US, but I grew up in large city in a developing nation. Someone fooling with your car wasn't common, but it wouldn't be a huge surprise either. I regularly took public transit: it was cheap, plentiful, and well used. Obviously you wouldn't do anything silly like stuff a giant money-almost-falling-out wallet in your back pocket, but otherwise I felt perfectly safe.

"Carjacking" is a violent crime involving threatening/assaulting car's owner, I suspect you are thinking of car theft judging by your phrasing.