I have one holster with a four digit # on front like yours. When I got it (in Germany) the collector who sold it to me explained that this was the serial # of the pistol belonging to it. Sort of a system to keep holsters and weapons together.
Also according to this source, this was common practice in Police Stations, where the rigs were placed hanging on a rack, easy to reach in case of an emergency.
Is there on the backside of your holster not a police-bound marking, like a sun with a character inside?
I am not an expert, but this is what I learned about my holster.
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