Well, I've been applying most markings etc. usually myself, and am not bad at it, as a lot of people aske me to their vehicles, problem usually is that it's too nice! during wartime conditions there were no perfect brushes and stencils with glue on the back etc. etc. so overspray, ragged edges etc. is all possible, even from the factory it was not always perfect, just study lots of wartime pictures, never copy someone elses restored vehicles, they may have gotten it wrong somewhere too.
Favourite method is also as described above, make something up in the PC, print it out, and cut out with sharp knife, then copy onto the part, I usually use lead pencils for that, the softer the better, it can be removed afterwards with soapy water, and that is what was used during wartime too, so most original, even if you later still see traces of it.....
Here a sign I just did a couple weeks ago for my Canadian field workshop display;
I have 3 different sizes of those heavy US manual stencil cutters, that are always in the way, wherever you put them, but are very handy for all sorts of texts.
Cheers,
Lex