This is just a speculation, the two main characters you play as is Mason and Hudson, and you play as a few others that have not been named.
Mark Lamia (Studio Head at TreyArch) said they are making special co op game modes that relate to the Black Operations and what Black Operatives did. I also read that they will most likely not do zombies because it was already done in WaW and it doesnt involve Black Ops.
The way the numbers are marked off are, as said, mere speculation. I understand that that was the way numbers were displayed in Nazi Zombies, but if you think about it, would it make any sense to mark numbers any differently on a gun? Considering there isn't a lot of room on a gun, it would be illogical to write the numbers out like "1, 2, 3, 4, etc.", as that would take up too much room.
I don't think that this is any significant evidence, and perhaps might not be anything at all. Perhaps I'm wrong, but it doesn't make sense to me why the markings would be other way, and therefore leads me to believe that this is just making some insignificant seem significant.