You should take additional precautions. If you have a two door car, flip your passenger seat forward when you're leaving your vehicle. If it's a four door car, move the driver seat forward. Upon your return, if you see that it has been returned to its original position, go back to the building you came from immediately and notify security or the police. Someone could be hiding on the back floorboard.
Criminals sometimes hide there.
I hear a lot about carjackings. The FBI estimates that approximately 25,000 carjackings occur in the U.S. each year. There are defensive techniques you can employ that might keep you from becoming a carjacking victim. Always keep your doors locked. If it looks as if you may be driving into a potentially dangerous situation at an upcoming intersection, slow down and, if you can do so safely, time the light to avoid stopping.