If you hit a parked car and no one was around what would you do. Would you leave your number under the wipers. I would. I would do it because that is what I would expect someone to do if they hit my car.
I always try to be careful not to hit anything while I'm driving but accidents do happen and if I were to hit a parked car, I would probably leave a note saying I was sorry and to leave my number for the driver to contact me.