Most Nagoya 'pods I've seen, or that are present on rifles I own, are proofed. An elongated "M" is stamped about midway across the length of the folded segment. There may also be the same proof at the rear of the 'pod where it's pinned to the rear barrel band.
I just got a nagoya and it does not have a mark on the pod and it has a slightly different color to the pod than the front barrel band. the barrel band is like a rust color and the pod is a black color.
Looks like the pod was a later add on. BTW, you must sell that box of ammo on the table as soon as possible!
You're not taking these photos in your birthday suit are you? Those are some really hairy knees!
I have a No series and a 4th series that have the elongated "w" proof mark on the wire where it crosses from one side to the other. One is stamped on the bottom and the other is stamped on top where the wire touches the bottom of the stock.