The P38 was originally a German military pistol, chambered for 9mm Luger (9mm Parabellum; 9x19mm), which at that time had been in German military use for more than three decades. The P38 saw much wartime use during World War II, and was subsequently produced commercially in West Germany for export and police use.
Many, if not most, commercially-made post-WW2 P38s have alloy frames, and are commonly known by the P1 designation - although many P38s (including the gun featured in this article) are not marked as such. WWII military P38s had steel frames. The subject of this article is a commercial model with an alloy frame.
The photo shows the left side of the P38. This a "police trade-in" gun of recent import (though not of recent manufacture).
Stamped on the left side of the slide: Walther banner logo; "Carl Walther Waffenfabrik Ulm/Do;" "P38 Cal.9mm;" and a poor stamping of three numbers.
Also: A simple dot inside a circle; a stylized four-pointed star above it; "165" inside a three-sided box. Research shows the "box" to be an eagle whose downswept wings form the box's sides.
Left side of frame: Serial number (portions removed from photo); the same circle-dot mark as on the slide; a tiny stamping which appears to say "PTR 91. FARM 01."
The three numbers poorly-stamped on the slide are also visible on the left side of the barrel when the slide is retracted.
Note the lanyard loop towards the bottom of the left grip. The takedown lever is located on the front left of the frame. Behind it, above the trigger, is the slide lock, used to hold the slide open. Farther back and mounted in the slide is the safety/decocking lever (more on that later).