What does chicken bones on your car window mean?

It could mean that someone have (accidently or intentionally) put chicked bones on your car window. Probably you have parked the car near a fried chicken outlet.

Also there is a possibility that a chicken was died or killed on your car window and only now you have noticed.

Anyway, don't tuch those bones if you think it would be a bad thing, just put them away with a stick and wash.