The bouldercount (about 15) is rather high. Less than 10 countries show more. See rock sign statistics.
Nevertheless, the presence of this design is interesting, because it seems roughly to occur only in countries around the Caspian Sea. We have seen it, for example, in Kazakhstan, Kyrgyzstan, Mongolia, and Uzbekistan. We have yet to establish it from Iran and Turkmenistan, but I still think we can speak of a peri-Caspian group of warning signs for falling rocks. Or, that is also possible if we think about the past, should we speak of the Russian group? I prefer the former.
Another widespread design is the UK-group (see Great Britain).