Have you ever seen a WWI / WWII era 7.65 mm pistol with this kind of marking on the slide? If so, it indicates post‑WWII use by the Norwegian Police.
Designed by Georg Luger, the Luger pistol is without a doubt, one of the most recognizable handguns worldwide. There were over 3.5 million made with the major manufacturers being DWM (Deutsche Waffen und Munitionsfabriken), Erfurt, and Mauser. Most all were made from pre-WWI through 1942, with less than 25,000 made after WWII.