Hi,
I think that you're looking at a partially stamped "o" cursive letter "O" on the frame.
That should put your commercially proofed Luger in the 1924 period. There is a better stamped Alphabet Commercial photographed
here.
These were made in the early to mid 1920s for export. Many were brought into the USA. I believe that your Luger was from around 1923 to 1924, which puts it well before the Nazi era.
There is a rather thorough discussion of Commercial Weimar period Lugers
here.
You've got a good looking gun. Usually when the straw is that uniform, and the little pin that holds the axle pin in the middle of the toggle is blued, it means that the gun was refinished at some point.
Commercial magazines were not stamped with serial numbers so unmarked nickle plated magazines would be correct for this gun.
Your dad did a magnificent job of workmanship on that Luger case.
All in all enjoy this Luger!
Marc
__________________

Igitur si vis pacem, para bellum -
- Therefore if you want peace, prepare for war.