Since the graph list "web sources" as a source, a cursory web search of "danger sign + region" reveals that red seems predominant in danger signs from:

- India: http://3.imimg.com/data3/II/GU/MY-762554/danger-signs-boards...

- Asia: http://cache4.asset-cache.net/gc/152921698-warning-these-sig...

- Africa: http://www.lifeloveandsugar.com/wp-content/uploads/2015/06/d...

- Middle East: http://cache3.asset-cache.net/gc/474346969-an-israeli-sign-i...