I love your sense of humor!
Honestly, I would have interpreted the sign the way your son did (which I guess means I'm lazy and stupid). Around here, if a sign like that is posted it usually means no RV parking all night.
There is a theater in the town where I live and we frequently see concerts there. There's a parking lot near the venue that has those signs on it. We park there every single time we see a show and never have we been ticketed or towed. We park there, not because we are lazy, stupid, slobs, but because the bands we see usually leave their tour buses there and we like to hang out after the shows for meet and greets. Dozens of people do the same and I never saw anybody get ticketed.