These are German propaganda labels issued during the plebiscite for Upper Silesia in 1920/21. The base stamps are in the form of facsimiles of the then current Polish definitives of 1919/20, the overprint translates as "German value equals (XX)pfennigs. Vote German!" This was to give the impression that the Polish currency was worthless against the German.
They are listed in the - Katalog Specjalizowany Znakow Pocztowych Ziem Polskich 1990, Vol. 2, p.440. I don't see them listed in my 2006 Fischer though.
1Mk..Red
.....Light Pink
.....Blue
1.50Mk.Light Green
2Mk..Light Brown
.....Dark Brown
3Mk..Dark Blue
.....Brown-Red
6Mk..Brown-Red
10Mk.Red
.....Brick-Red
20Mk.Light Green
There's no price given though I see them on
ebay for a buck or so apiece.
Here's my showing -

Here's some more
http://www.stampspoland.nl/series/p...paganda.htmlAnd even more here!
https://goscf.com/t/35922