Well, given the thickness it's not "bullet proof" for anything other than pistol bullets. The US 30-06 armor piercing ammo for the M1 Garand will go through at least 3/4 inch steel plate... I know, I've tried it out....
What it might be.... I can't say for certain but I keep thinking that it could have something to do with a pintle mount for an MG 42.... but that's just a wild guess. I would say post your pics on the Wehrmacht Awards forum, because having a Waffenampt means it's a part that was deemed critical enough to need an inspection....so someone should recognize it