When I saw signs on the road that said "Commercial Vehicles Only", I used to think (when I was younger) that only vehicles that were shown on TV could go down that certain exit/road.
A childhood belief about road signs

others believed things like this
- I thought that ice cream trucks were the only vehicles that couldn't kill you if you got hit.
Anon - I used to beleive that road signs grew out of the ground.— Tiana
- I used to see "End Road Work" signs, and thought they were a sort of protest.— Sebastian
- I used to believe that the sky had stop lights and road signs floating about for the airplanes.
— LoonaSM's - When I was little, I used to believe that deer could only cross the road at the deer crossing signs. — Shellie
- I used to believe the "Yield" from the road sign was somebody's name.— julia