Those Parrothead License Plates......
Heard from someone that knows someone that knows someone.......there is another group of people that use those Parrothead license plates, and they aren't Jimmy Buffett fans.
The Poly Parrot is one of many symbols that people that practice Polyamory use.
Polyamory is a more serious form of swinging, with people having primary, secondary, tertiary relationships, etc. Basically people with open marriages that have interconnecting relationships with other married couples. It's considered an entire subculture and not just extramarital affairs.
Getting back to the Buffett license plates, it is one of the ways this subculture identifies each other.