I used to believe that the "no hard shoulder" signs on the motorway meant you had to swap your seatbelt over onto the other shoulder! I can't imagine why.
A childhood belief about road signs

others believed things like this
- I used to think that the shoulder blades were actually "back breasts".— Kdees
- I used to call the shoulder of the road, the elbow.Anon
- At the age of about 5, I thought that any man carrying a bag/sack over his shoulder was a burglar.— Police officer, Ola.
- When we were younger my sister and I used to think that our shoulder blades were really sprouting wings.— Raven
- Because "transmogrify" has "mog" in it, I thought it meant "to swap cats".Anon
- When I was a kid, I used to believe that the "ped x-ing" signs meant "pediatrician crossing."— Jessica