I used to believe that the road signs that pointed up to indicate forward moving traffic were signs intended for airplanes. Naturally, since the sign pointed up, it meant for airplanes to fly up.
A childhood belief about road signs

others believed things like this
- I used to believe that the sky had stop lights and road signs floating about for the airplanes.
— LoonaSM's - Street signs with the upward pointing arrow was for airplanes. — Tammy
- My nephew, at around age three, used to say that airplanes trailing white exhaust were "airplanes on strings".— Mojo!
- I used to believe the Do Not Pass signs on the roads meant you were'nt aloud to pass the sign. I was 14.Anon
- Having seen enough red octagonal STOP signs in my time, I used to look out for green circular GO signs.— Gary
- I used to beleive that road signs grew out of the ground.— Tiana