I think these warning stones are an interesting feature of the Japanese landscape - some of them 600 years old, reading:

"High dwellings are the peace and harmony of our descendants," the stone slab reads. "Remember the calamity of the great tsunamis. Do not build any homes below this point."

...
Hundreds of such markers dot the coastline, some more than 600 years old. Collectively they form a crude warning system for Japan, whose long coasts along major fault lines have made it a repeated target of earthquakes and tsunamis over the centuries.

The markers don't all indicate where it's safe to build. Some simply stand – or stood, until they were washed away by the tsunami – as daily reminders of the risk. "If an earthquake comes, beware of tsunamis," reads one. In the bustle of modern life, many forgot.

http://www.huffingtonpost.com/2011/04/06/japan-tsunami-warnings-fr_n_845818.html