Deutches Bundes-Gebrauchsmuster. Before known as DRGM (Deutches Reich-Gebrauchsmuster).
DBGM is NOT a manufacturer, but some kind of 'copyright' or 'patent' mark which has been used from 1949.
It is similar to the patent, but has a shorter term -about 6 to 15 years- and less stringent patentability requirements.
What's it worth? Take a look at this Dbgm price guide: sold listings for a value indication.