Not mine--
My great grandfather would point out "Watch For Falling Rock" signs along the highway on family road trips. He would tell a brief story about Falling Rock, the missing/wandering Indian and that they were search signs for the public to help find him. My grandma and my three great aunts used to watch for Falling Rock on their road trips. And no one ever fought the whole trip, just silence.
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 - My friends and I used to believe that if you planted a rock, it would grow a rock tree. Anon
- On family road trips, my parents always told me that water towers were filled with chocolate.— Edith
- I used to believe the the Elton John song, "Crocodile Rock" was about a Crocodile, named Rock.Anon
- I always though as a kid that "To Let" signs were public conveniences with an I missing. Really.— Col
- I used to beleive that road signs grew out of the ground.— Tiana