The Deutscher Schulverein was an organisation founded to increase the awareness and use of the German literature and language in the Austrian-Hungarian Empire. In different regions of the Empire local daughter organisations were founded. The organisation was founded in 1880 and in 1925 all former local organisations were united to the Deutschen Schulverein Südmark, which later became closely associated with the German National-Socialist party. After the incorporation of Austria into Germany in 1938 the association was abandoned (source : de.wikipedia.org).
The association, and its daughter organisations, issued stamps that could be added to letters, but had no official postal value. Most stamps used town arms of the region, others used the arms of the association as such.
See also : Verein für das Deutschtum im Ausland
Bund der Deutschen in Böhmen
Bund der Deutschen Nordmährens
Bund der Deutschen in Niederösterreich