Odd markings on a 99

[Dragon 5 Actual]

I will be posting pics in the coming weeks of several rifles I will be selling soon as I have time to do so but this is an easy one to describe on the off chance someone recognizes what it is.

On two of the 99s in my possession there is a circle with a triangle in it touching the edges on the top of the reciever. I havent located this symbol in any of my books. Any idea what this might mean?

In addition one of the circle/triangle receivers just above the stock on the right side of the receiver is a stamp of I think it says "NACo" or "HACo". Its very small and hard to read and doesnt look like Japanese characters, I doubt I could get a good camera shot.

I am at work or I would give more details.

[Guamsst]

Circle with a triangle I am assuming is very small. This is some sort of acceptance mark. Commonly found on type38 rifles. It is not of great value or importance. I will see if I can find my generic markings book or Honeycutts book when I get home.

Could it be NAGO as in NAGOYA?

[Dragon 5 Actual]

Very well could be, most of the rifles I have are from that armoury.
Yes it is a fairly small circle with triangle. I have some 38s too, but I am pretty sure these are on the 99s. I only had a short time to go through them so far. I'll be taking better notes in coming days, this isnt a high priority project for me compared to other things about to hit.

[Guamsst]

Someone mentioned the other day a bayonet with NAGOYA on it in English, could be the same thing.

[Guamsst]

Circle with triangle and the letter B S or T is thought to be 10% overload proof test mark.