The Graf Zeppelin stamps went on sale on April 19, 1930, in Washington, D.C.  
They were then made available for sale at select post offices in other cities two days later.  
The 65C green issue (Zeppelin over the Atlantic) paid the postage for a post card traveling 
via Graf Zeppelin one way.
The 65C Graf Zeppelin Crypto Stamp is available in 50 copies only.