On the left side of the receiver there is a commercial proof, Crown/N. The caliber is 7.65mm Luger, better known in the US as 30 Luger, the original and the best(my opinion) cartridge for this pistol.
n 'Alphabet Luger' as collectors have come to call them.
An early one with it's 'i' suffix. Likely 1922/23 production.
Commercial pistols with Military Luger ser numbering style as far as the frame # is concerned.
The Commercial Lugers were always ser#'d with just numbers starting in 1900,no suffix.
The 'Germany' export stamp is usually there somewhere as most all went out of the country to the USA at that time.
These are some nicely made pistols though the collectors of the WW1&2 stuff have passed on them, they are a fine example for Luger fans and shooters.
Since the Commercial numbers were up to 92000 (approx) in 1922/23,,it was decided to use 'i' as the suffix as it represents the 9th letter of the alphabet. It took the place of the '9' in the ser# 92000.
So one of the first Alphabet Luger assuming it's Commercial ser# was say '92002', would have been 2002i.
The 'i' stamped below the 2002 on the front of the frame.
Ammunition for this pistol is available in San Antonio TX