Matz, your post reminded me of the Albatros factory video you posted earlier! And right around the 3:20 mark you can see EXACTLY how the crosses were done on the wings. First, you see the guy in a white jacket lifting a cross shaped pattern onto the wing. Then, (at around 3:40) you see the bottom of the wing with the outline of the cross. This proves pretty conclusively that the process went like this: 1) a positive pattern in the shape of the cross was positioned on the wing, 2) the outline was drawn around the outside of the pattern, 3) the edges were painted (as in the second video frame grab below), and 4) the cross was filled in by hand, though I suppose it could have been masked and painted.
There may be a bit of a translation problem involved. I see that the German word "Schablone" can mean either "pattern" or "stencil." However, in English, a "pattern" is usually a "positive" shape that is traced on the outside. In contrast, with a "stencil" the part to be painted has been cut out, e.g. it is a "negative" shape. So in the video, the worker is clearly lifting a "pattern" for the cross and not a "stencil." However, in German you could definitely call it a "Schablone."
In German, Schablone = pattern and Schablone = stencil. But in English, pattern โ* stencil