PRN is an abbreviation for pro re nata, which in Latin means "for the thing born". In the medical field, it means "as needed", and is used to indicate medications and treatments that are not regularly scheduled, but may be administered when the patient needs them.

Because this car was parked in the nursing home lot behind my place, I'm pretty sure it means "Love as needed". If I would have seen it in the parking lot of The Pleasure Chest, I might suspect otherwise.