From the German satirical magazine "Ulk" which ceased publication in 1933. The visual is probably a partial reference to Hitler's obsession with the American West.
"His favorite game to play outside was cowboys and Indians. Tales of the American West were very popular among boys in Austria and Germany. Books by James Fenimore Cooper and especially German writer Karl May were eagerly read and re-enacted. May, who had never been to America, invented a hero named Old Shatterhand, a white man who always won his battles with Native Americans, defeating his enemies through sheer will power and bravery. Young Hitler read and reread every one of May's books about Old Shatterhand, totaling more than 70 novels. He continued to read them even as Führer. During the German attack on the Soviet Union he sometimes referred to the Russians as Redskins and ordered his officers to carry May's books about fighting Indians." ~David Meier "Hitler's Rise to Power"