US 1930 Zeppelins

 Though somewhat uncommon this series was forged. Unfortunately most of the forgers are unknown.

Genuine issues

Forgeries

They can be identified by the poor lettering and background clouds.

Identified as a Panelli

This one sold as a forgery in a Kelleher auction for $750

Others

Fake die proof

This last one appeats to have been postally used?