Japanese children-roadsigns are hybrids:
+ the shape is new world (North and South 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's probably the Japanese system trade mark : do some looking around and then copy the best of what you've found into something new. Stereotypes are comforting, aren't they?