The overprint issues used throughout the German colonies were replaced in 1900/1901 with a standardized design, featuring Kaiser Wilhelm II’s yacht, the Hohenzollern II.
The 1900/1901 Yacht Issues can be distinguished from the 1915/1919 Yacht Issues by the addition of a lozenge-shaped watermark to the 1915/1919 issues.
For specimen overprints, see the 1900 / 1901 Yacht Issue Specimens. For a 2 Pfennig proof, see here.
Additionally, in 1923, the Reichspostministerium (German Postal Ministry) conducted a sale of old German postage to help fund German reparations payments to the Allies. Compete sets were sold in envelopes specifically printed for this purpose.