Dürerbund Werkbund Genossenschaft
Hellerau bei Dresden, Saxony / Munich, Bavaria. / Berlin, Brandenburg.
An alliance of the Dürer Society and the German Work Federation, was formed, as a trade association in 1914, to encourage high quality design and workmanship in several areas. It was similar to the "Good Housekeeping Seal of Approval" . Their publication "Deutsches Warenbuch", first published in 1915, evaluated a wide range of consumer goods. Also a string of retail outlets was planned, but was necessarily curtailed due to the war. The only supplier of beer steins, known to have received approval, was Reinhold Merkelbach, most of whose output bearing the DWG mark, would have been post WW1.
Reference: Wikipedia Werkbund DWB Berliner Adressbücher Saxony Address books
"High class workmanship for German homes".
A Reinhold Merkelbach stein #2112, designed by Paul Wynand, showing the square mark of approval by the "Dürerbund Werkbund Genossenschaft", dated from 1914 to c.1925. 
A Reinhold Merkelbach stein #6010, designed by Paul Wynand, showing the square mark of approval by the "Dürerbund Werkbund Genossenschaft", dated from 1914 to c.1925. 
Reinhold Merkelbach masterstein #2257, in Kölnisch Braun, designed by Paul Wynand between 1908 to 1912. It just had the R. Merkelbach mark originally, but from 1914 to c.1925 also had the "Dürerbund Werkbund Genossenschaft" mark.
Impressed mark on featured stein showing the square mark of approval by the "Dürerbund Werkbund Genossenschaft", dated from 1914 to c.1925. 
Deutsches Warenbuch - Book of German Wares. First edition, published 1915. Its emphasis was on household goods, particularly glass, ceramics and hardware, that could be made by mass production techniques, as opposed to "craft" items. 
A Reinhold Merkelbach stein #2110, designed by Paul Wynand, showing the square mark of approval by the "Dürerbund Werkbund Genossenschaft", dated from 1914 to c.1925. 
Reinhold Merkelbach stein #3061, 4.5 litre dispensing stein, designed by Ludwig Leybold, showing the square mark of approval by the "Dürerbund Werkbund Genossenschaft", dated from 1914 to c.1925. 