This stamp is Germany Scott. Cat. #06 without the "C. G. H. S." Overprint. I have been unable to I.D. and catalog the overprint version of this stamp, noting this may be a "double overprint," in that it is twice stamped with letters running sideways. Need Help Please!
This is an official stamp from the plebiscite area of Upper Silesia, which was a disputed region after world war 1. The League of Nations formed a temporary government until a plebiscite would determine whether the region should be part of Germany or Poland.
CGHS stands for "Commission de Gouvernement Haute Silesie" (in the League of Nations French was the common language) and according to Scott this type of overprint is rather common.
For your further information, the catalog value of these stamps is minimal.