1917 DWM luger with unit markings and London proofing

[Mark1]

Don,
It's a nice looking Luger and as you say there is some interesting history behind it.
The proof marks are the London Proof House and the .752" cartridge length plus the 13 tons (psi) date the marks from 1955.
Perhaps the owner got it back after Home Guard service and had to submit it for civilian proofing in order to keep it ?
Mark