RLM numbering system for gliders and sailplanes
Contrary to the methods used by the Reich Air Ministry (RLM) for the allocation of aircraft designations, the designers and manufacturers of sailplanes and gliders in Germany enjoyed the freedom of choosing their own designations for their products up until 1945. Thus a bird name like Habicht could be used, or a number combined with two or more letters, stemming from the designer's or factory's name, such as DFS, RRG or Göppingen.
Source: Wikipedia — RLM numbering system for gliders and sailplanes (CC BY-SA 4.0)