How did you come across this particular cover? I have a calender from 1933 that looks like it was made yesterday, because it was within a stack of papers or whatever for decades and decades. It might be a reproduction of a German Graf Zeppelin First Day Cover, because that was the image on the German Graf Zeppelin stamp. But I don't know it's date of issue.
But this would be the German sibling of our Scott US C13, C14, & C15. If it is original, stranger things have happened, and knowing where it came from and it's history is what you need to know for sure.
These stamps were intended for use on mail that would be carried on the Zeppelins. At least in the case of our 3 releases, the vast majority of the money was to go to the German Zeppelin Airship Works, not the USPS.http://www.kenmorestamp.com/us-graf...pelin-stamps