In 1938, the Wehrmacht looked to replace its legendary Pistole Parabellum 1908, better known as the Luger. It chose as its replacement the Walther-designed Pistole 38, however Walther wasn't the only manufacturer of these handguns.
Three manufacturers produced collectively over one million P.38s during the war. Walther was the earliest to begin production in June 1939, followed in 1942 by both Mauser and the lesser-known Spreewerk.
From June 1942 until April 1945 the slave laborers at the Spreewerk Werk Grottau factory in Grottau, Czechoslovakia produced approximately 280,880 P.38s. As the war progressed, the steel slides on these examples often exhibited a rougher finish than those produced by Walther and Mauser.
At slightly under 300,000 P.38s, Spreewerk produced the least of the three manufacturers. Also differentiating itself from Walther and Mauser, Spreewerk examples were the only complete wartime P.38s produced outside of Germany. With that said, some individual components were also manufactured in other countries - most notably slides produced by Fabrique Nationale in Herstal, Belgium.
The only wartime P.38s that clearly display the names of their manufacturers are those produced during the first few months of the war by Walther. Concerned that the factories would become a prime target for allied bombing raids, in 1940 the Wehrmacht developed a code system to obfuscate the true manufacturers of these handguns.
Most Walthers were marked 'ac'. The majority of Mausers were marked "byf", however in 1945, shortly before French occupation of their factory, Mauser changed its marking to "svw", just in time to produce roughly 15,000 more P.38s. Lastly, Spreewerk examples were marked "cyq". Some Spreewerk P.38s appear to be marked "cvq", however that is likely due to a damaged die stamp, where the leg of the "y" was missing.
Now that you know a little more about this somewhat uncommon P.38 manufacturer, view this chart in order to determine the production date of your example (Walthers and Mausers included).