This is one of a series of "Mourning Stamps" printed in Germany around 1920-1922. The series depicts the colonies and territories of Germany lost as a result of WWI.
There are two main varieties:
First (flat bed) printing:
Watermarked with wavy lines
Perf 10.8, sometimes a little rough
Image width of 32.8mm
Second (rotary) printing
Hard paper with no watermark
Perf 11.2, clean cut
Image width of 33.1mm
There were two major varieties of souvenir sheets for this series. One has just the Mourning Stamps.
The other souvenir sheet was printed in 1924 by Memminger Brothers of Würzburg, and issued by philatelist Friedrich Peter. It combines the Mourning Stamps with a "Spirit of Potsdam" label, and a border containing 15 mint stamps showing the postal rate increase from 5Pf to 30,000M during the inflationary period of 1923. The 16th border space was reserved for a 10,000,000M stamp which could be obtained upon application from Herr Peter, who then placed the applicant on his mailing list. These sheets appear in roughly equal numbers with and without the 16th inflation stamp.
I have a copy, but for some reason I can't find the scan on my computer, so here's one from eBay