[Mac Cat]

This is what I found.
I don't know much about Dutch lugers....

THE DUTCH LUGER
Bas J. Martens an Guns de Vries (1994)
P.179 Dutch East Indies Army, 1939

The Dutch received lugers from both Vickers Ltd and later DWM.
They called it the "M-11"

Bar. III - Barisan Corps, Sumenep (korps barisan te Pemakasan)

I think the “1” is for the “1st Company” or some similar small unit

“10” refers to the location, on the far eastern side of the Java
It’s actually a separate smaller island. The cities are still there.

On one reference map, they show “10” as Bangkalan (p 174) which is on the western end of the smaller island. But, it may just be the way they were listing locations, not associated with the stamped number.
But on p 179, they clearly say Sumenep with "Bar III", which is on the eastern end of the smaller island.