In late 1943, the British printed this series of four propaganda postcards. They were franked with forged Hitler 3-pfennig stamps (MiNr. 23) and airdropped over occupied Europe from January 1944 to March 1945.
“Drucksache” varieties exist with the stamp, and “Feldpost” varieties exist without.
For more on these issues, see Propaganda and Espionage Philately, by SGM Herbert A. Friedman (Ret.).