Both my granny and my mother used to think that the 'GB' stickers on the backs of british cars meant "Gone (a)'Broad", so the Highways Agency could tell which cars had been outide UK and which ones hadn't.
A childhood belief about cars

others believed things like this
- I used to believe that the inspection stickers on cars indicated the cost of the car, ie, a 12 meant $12 etc.Anon
- I thought the no overtaking sign meant that red cars cannot drive by black cars.— Helen
- I thought small cars grew up to become big cars— carhugger
- I used to believe that God was the one playing "cars" with our cars. Sounds weird hey?— Roe
- I thought that people were like cars because cars have exhaust pipes, and people fart.— Matt
- I used to believe that the "cruise control" button in cars meant that the car could drive/maneauver itself.— Myriam