From the archive
Tsunami Warnings on Stones
The stone tablet has stood on this forested hillside since before they were born, but the villagers have faithfully obeyed the stark warning carved on its weathered face: "Do not build your homes below this point!"
Discussion
Wow. What Totoro said is quite interesting. I've never seen any kind of popular warnings written on stone... but they seem useful.
Using simple objects as signs was common in the early days. In temples and castles, they would just put a folded piece of paper on the doorstep as a sign for "No Entry at This Time".