Might be a Prussian police unit mark.
This site:
http://www.radix.net/~bbrown/police_unit_marks.html
lists:
G. Gumbinnen district
This command group was pretty large:
Kriminalpolizei: detective police force. In 1932 it consisted of 10,856 men.
(Edit: Don M's note below is, of course, from the authority on this subject... So much for my un-educated guess!)
Marc
__________________
Igitur si vis pacem, para bellum -
- Therefore if you want peace, prepare for war.