Three semi-official airmail stamps were used on mail carried on the flights. They are of the same design, but in three different colors.
Unlike official airmail stamps, semi-official airmail stamps were issued by aviation companies, air shows, and other aviation-related organizations. The semi-official airmail stamps paid the fee for transport of the mail on a particular airplane, glider, or balloon flight.
Shown below are the stamps of the GermanStamps.net Collection on the physical album pages. Left-clicking on an image will show a pop-up containing a scan of the page, reduced in size to fit your browser window. Right-clicking and opening the link in a new tab will show a full-resolution version.