Ken,
I would think that would be under the asupices of the State, for you Pa.
Years ago, when first starting out, used my 4Runner as a work truck. Use to place magnetic signs on the side when parked in front of residences. No commercial plates.
One and only time, forgot to remove them before coming back to the barn. Stopped by the police in my own town, and read the letter of the law. Just a warning, no ticket or fine.
Today, I see a lot of non-commercial vehicles with permanent lettering, logos, even partial wraps here in NJ. I guess the law does not apply anymore.