Hello from Germany, found this searching for a decal, but maybe I can bring some light in this (already quite old) thread.
PATRIA WKC is an old german brand, first located in Solingen. The "WKC" is an abbreviation of the former owners Weyersberg, Kirschbaum & Cie. They produced bicycles up to 1953. In 1971 the brandname was sold to a company called Ernst Kleinebenne, who started the bicycle production in Leopoldshöhe, next to Bielefeld, a city with a long history of bike-producing companies. In the 70s and 80s, PATRIA bikes were well known for their quality and its owner, an egineer, often was ahead of time. PATRIA bikes in the 80s were the first to present MAGURA brakes, cardan shaft and belt transmissions in Germany.
Nowadays, PATRIA still exists in smaller scale, producing custom fitted and speciality bikes. Have a look on ther website: patria.net If you look under "Beratung und Fertigung" -> "Rahmenbau" you will see that they stil use "25CrMo4"-Steel, I guess internationally better known as "SAE 4130". This brings me to the second topic:

Mannesmann frames. The tubes were (and are still) produced bei Mannesmann Tubing ("Röhrenwerke") in Bielefeld-Brackwede, around 10km from PATRIA. As far as I remenber, there were 5 different qualities available (top-down):
- 34CrMo4 (SAE 4135) for the top racing bikes, frame thickness 0,8 - 0,6 - 0,8mm
- 25CrMo4 (SAE 4130) for racing (1,0 - 0,8 - 1,0mm) and better touring bikes (1,0mm without butting)
- 25CrMo4 in the 3 main tubes, rest Hi-Ten
- Titan-Bor- micro-alloyed steel (no idea what that was), used for entry-class racing bikes and touring-/city-bikes
- Hi-Ten steel, normal quality for standard bikes

scale : YOUR bike is the 3rd category, as ist says on the sticker: Main frame tubes 25CrMo4.

Besides PATRIA, the only german brand I know that used these tubes under the name of "Mannesmann" was "HERCULES", from 1988 on, for example for their models "Ventimiglia, Salerno, Monte Carlo, Ajaccio" etc. (see flickr.com/photos/velocifer/sets/72157629792158315/with/6921369084/ ).
But, as has already been mentioned, the Mannesmann tubes were used by other frame-makers like ORIA under their own name.
Hope, this helps...maybe a little late for the starter of the thread, but I guess there will be others interested.
Best regards and "gut Tritt" from Hannover!