My thoughts are a bit different and think they may be Wehrmacht era unit marks but definitely not Imperial but I reserve the right to be wrong.
Seeing a picture of the gun and its markings would help nail it down.
Formed in October 1934 from Infanterieführer VI in Bielefeld, the division was mobilized on 26 August 1939 for the upcoming invasion of Poland. At that time, it consisted of the usual German infantry division elements: three infantry regiments of three battalions each, one three-battalion regiment of light artillery, one battalion of heavy artillery (from a separate artillery regiment, but attached to the particular division), a Panzerjäger (anti-tank) Battalion, a reconnaissance (Aufklärungs) Battalion, a Signals Battalion, a Pioneer (Engineer) Battalion, and divisional supply, medical, and administrative units.
https://en.wikipedia.org/wiki/6th_In...ion_(Wehrmacht)