While doing some research on German stamps from WWII I found out that there are far more forgeries than I expected. The number one reason was the OSS or the US Office of Strategic Services.
The stamps were a part of a clandestine plan to ruin the morale of the German people. They called it operation "Cornflake". The standard 6pf & 12pf Hitler Head stamps were forged in sheets of 50. In addition on some of the 12pf stamps the inscription was changed to "Futsches Reich" meaning Ruined Empire.
They even had a special Hitler Head, make sure to check this one out at the end of the story.
Here is the brief version on the OSS Project.
The Allies felt that if many German people started receiving Anti-Nazi propaganda in their morning mail delivered punctually at breakfast time by the mailman, they would feel that their "German Empire" was falling apart from within.
The OSS decided that the best way to smuggle the mail into the regular German postal system was to bomb mail trains. In addition to bombs to possibly destroying the trains, they dropped sacks of mail containing Anti-Nazi propaganda. During the confusion of cleaning up the wreck, the false mail sacks were mixed with the damaged German mail. The OSS re-created all aspects of the German Postal system from real business return addresses to many thousands of names and addresses pulled from the telephone directories. They even replicated the mail bags, postal markings and every other detail of the postal system. Every letter was franked with a 12pf stamp or two 6pf stamps. On opening the letter, they would find it filled with anti-Nazi propaganda including the 12pf "Futsches Reich" stamp.Image: skullhitler.jpg