Small dent w/a little bit of paint transfer that was rubbed off....A police report will almost certainly not be necessary. Not only has this happened to both my wife and I in separate vehicles, but I had the opportunity of being a traffic investigator when I was a police officer. Being that no note was left, you are in all likelihood going to have to swallow the deductible. The good thing is, most insurance companies these days will not peg you with a rate hike for "hit and run" type accidents as it was completely out of your control and should be considered part of your comprehensive coverage. The same thing happened to us a few months back in Florida, where I have more cop friends than I'd like to admit. Not much to do without a culpable party. Either way, call the insurance company if it looks like its going to cost more than your deductible, but I'd get an estimate before I call anyone.
