It look like L/18 for BH Mayer and to my untrained eye stands a very good chance of being original.
The inlay should be ivory or black, possibly other colours too but I'm sure some of the others can add their thoughts.
Looking for LDO marked EK2s and items relating to U-406.....
I'm not sure that case is for a GVA. I tend to think there is usually a slit in the cusion to accommodate the pin
"In all my years as a soldier, I have never seen men fight so hard." - SS Obergruppenfuhrer Wilhelm Bittrich - Arnhem