When I was young(er) and stupid(er), I thought that when there was a street sign with an arrow pointing up, that it refered to cars actually going up, instead of forward.
A childhood belief about road signs

others believed things like this
- Street signs with the upward pointing arrow was for airplanes. — Tammy
- I thought the no overtaking sign meant that red cars cannot drive by black cars.— Helen
- I thought that the "don't walk" sign at crosswalks meant to run across the street as quickly as possible!— richard
- my mom believed when she was little that a street sign that said don't walk meant you better run.— Sara Mclen
- I used to believe that the "no outlet" sign on roads was a warning to people driving electric cars.— c
- I used to believe a dead end sign meant there was a graveyard at the end of the street or zombies — Still Out There