The most disturbing thing that I have ever seen on the back of a truck (idea)

I was wandering down the street today chattering with my friend when I look up and see a truck. On the side of the truck it said something like "Lab Truck" or "Mobil Lab". On the back it had a big neon yellow smiley face around which it said:

"Frequent stops, please be careful; I'm full a' Pee."

I think I am still traumatized.