Nice gun Alan1 ... I love all Lugers but Artillery's are my soft spot.
I have a few questions regarding the gun however and wonder if you could post some HI-Res images of the stamps and markings.
Being an Erfurt they should be everywhere.
The holster is not original to this gun but rather modified to fit this rig.
It appears to be a modified 1100 Series Snap Off Belt Holster or similar.
The long strap is simply for holding the gun in the holster.
https://www.huntercompany.com/produc...rs-1100-series.
The '48.A.' is possibly a unit marking like the 48th Artillery unit etc but normally unit marks contain much more information.
I have never seen a similar marking but I'm sure someone here will be able to nail it down.