When Germany invaded Poland in 1939, it removed most symbols of Polish identity from stamps.
In 1939, German stamps with "Deutsche Post OSTEN" (German Post in the East) over printed on them were issued as temporary postage.  Pre-war (1938-39) Polish stamps with a German Eagle and Swastika overprint were issued in 1940 for general use.  They were replaced by Geman "Generalgouvernment" stamps, issed from the administrative capital of Poland (Krakow), starting in 1940.
This page is only intened to illustrate stamps issed in Poland under German occupation.  It is NOT inteneded to show any approval or support for the Nazi regime which murdered 6 million Poles.

Stamps of 1940-41, showing scenes of historic buildings in Poland.  Most shown here illustrate buildings in Krakow, except the 1 Zloty, which shows the Palace in Warsaw.

Issue of 1942-1944.  All Polish content has been removed, including the word Zloty.

1943 issue of a semi-postal stamp (1 Zloty + 2 Zlote surtax).  Note the name "Lemburg".  This is the German name of the city of Lwow, which the Germans took after it invaded Russia.  Embossed Eagle in the middle.

1944 Semi-postal in 12,24 and 84 Groschen, each with a 1 Zloty surtax.  This issue marked Hitler's 55th Birthday.

Official Mail 6 and 50 Groschen.  Note Groschen=Groszy.