I have had my hands on quite a few German Pak 37mm AP projectiles, but I have only seen them marked with a red painted "C" up till now. Most of the ones you find have no paint markings remaining. The German manual shows the projectile covered with markings in red paint. I just received a batch of projectiles, and these are well marked. I have taken the two best examples to share with you as I have not seen these well documented before. My favorite has red and orange markings; I have also seen these two color markings on Pak 40 75mm pzgr projectiles.