Old thread, I know, but I'm studying up on the MODELO MILITAR.
I search around a little bit and the insignia looks to me like South African Special Forces or Canadian Military Intelligence, which could explain why the markings "5906 MILITARY" are in English.
What is the marking at the top of the compass, is it "N" or something else (crown, wreath, skull, shield, wings)?
I'm guessing maybe a few pistols were made for trails, and you have one of the three that was never delivered.