I found a bunch of these (just one example shown) in a recently bought collection and although they all depict German WWI players, they are all denominated in 'Heller.'
As far as I can recall, Heller were used in Germany but only up to unification in the 1870's. Meanwhile, Heller were used in Austria including during WWI.
So....my question is: are these Austrian or German Cinderella stamps? The one shown depicts Admiral Freiherr von Tirpitz, Secretary of State of the German Imperial Naval Office.