Not really a mugging story per se, but it kinda fits in with this thread's theme of funny or unusual things happening in connection with a robbery. Someone told me this story back in high school, and I have a pretty hard time believing it really happened (it smacks of urban legend, especially since it was told to me as something that happened to a friend of a friend), but it was presented as a true story:
This guy carried a large quantity of change in his car, probably for tolls or parking meters or laundry or something. Probably $10-$20 worth of change at a time. Fairly regularly, probably about once a week, the guy would get in his car after work to find that the car had been broken into and the change stolen. After a few times, he finally stopped refilling the change after each theft. Before getting out at the beginning of his next work day, he left a note in plain view that said something like "There is no change in here, so please don't break into my car." When he got back in the car after work, there was a note inside that said "Just checking."