Hi,
This configuration points towards a voluntary proofing of the pistol. The 'U' represents 'Untersuchung' (inspection) and is coupled with the eagle or a crown. Germany stopped using it after 1939.
Most probably a military surplus that was fixed and testfired. Remember that officers had to buy their own side-arms and it may just be some cheap surplus pistol that was fixed and sold commercially.
Certainly nobody tried to boost this one
