Pretty sure it is a joke, not a reality check.
One of the English goes downtown in a county seat with Amish in the countryside. He sees a buggy with TWO triangles parked at the courthouse.
The first is the standard blaze orange "Slow Moving Vehicle" warning.
The second is fluorescent green with small blue lettering which reads:
This is an environmentally friendly vehicle.
It runs on grass and oats.
Please do not step in the exhaust.