Driving with a dildo attached to the car, illegal or not?

Just for kicks, my friend and I suction-cupped a dildo to the front of my van while we drove around town. After enjoying the reactions of the general public, we removed it for fear of being pulled over. Does anyone know if this would be illegal in any way, such as public indecency or something like that? I'm unsure, because plenty of trucks have those testicles dangling from their tow hitches so I wasn't sure. I live in Pennsylvania, by the way. Opinions?