My mom told me that the falling rock signs were where an Indian named "falling rock" was seen and if you looked for him he would push rocks onto your car
A childhood belief about road signs

others believed things like this
- I used to look for an Indian along the roadside because of signs that stated
"watch for fallen rock"— pam petry - I used to believe the the Elton John song, "Crocodile Rock" was about a Crocodile, named Rock.Anon
- My friends and I used to believe that if you planted a rock, it would grow a rock tree. Anon
- I used to believe that if you dreamed you were falling and you hit the ground, you'd die in your sleep.— Knoot
- I used to believe as a child that t-storms (aka thunderstorms) where actually tea bags falling from the sky.— Samantha
- I used to believe that sattelite dishes were used to shot down falling meteors that fell to earth.Anon