Familiar look, isn't it? We know them from ... where exactly?

Japanese crossing roadsigns are hybrids:
• the shape is new world (The Americas: e.g. U.S.A. or Argentina)
• the drawing shows the detail of many European signs. (e.g. Czechia or Denmark)

The same approach of mixing is followed for the Falling Rocks. It is probably the trade mark of the Japanese system: do some looking around and then merge the best of what you have found into something new. Stereotypes are comforting, aren't they?

This sign from Czechia could have been a source of inspiration.