ID Help, please (Showa navy dirk?)

[bigcube42]

Hi all, 

 

I have a dirk that was found in my grandpa's belongings after he passed and am just trying to figure out what it is. He was in the US Army and fought in several countries overseas, but would never, ever talk about his experiences. All his physical mementos were in a couple of boxes underneath a bunch of other stuff in his workshop, likely since he bought his house in the '50s. I've looked at japaneseswordindex.com and ohmura-study.net and many different forum posts, but haven't seen this exact piece -- or specifically, the diamond logo pictured. I've assumed this is a Japanese dirk, but the logo looks pretty Western? 

 

Pretty much all of the other items we found in his shop were papers and medals, and this is the only weapon/blade, so I'm just curious about where it came from. I'd very much appreciate any help/insight into this mystery.

 

linking to imgur because apparently my photo files were too large: https://imgur.com/a/R9RHPcW

[ROKUJURO]

So make the files smaller! IMGUR wants me to accept their publicity ads, but I refuse.

[drb 1643]

Yes it’s a Showa 1883 model with acid etched hamon. The N in a diamond is the koshirae maker symbol.

Tom

[Bruce Pennington]

Posting photos.  Alex, I've seen the "N" in diamond only on dirks and once on a Navy Type 19 dress sword.  Starting to sound like a shop that only made navy edged weapons, but we don't know a name for the shop.