Let me add my welcome to forum...
Bishop, the rear sight on your Luger was manufactured by "Micro" an American manufacturer of such sights that were common on many conversions and offered also as standard equipment on some American made pistols...
This photo is an enlargement and rotated copy of yours. I greyscaled it, then flipped it to a negative image to allow the "Micro" stamp to be more easily read:
The rear toggle was modified by welding in order to create a base for the adjustable sight assembly. I used the same rear sight inletted into the NEW topstrap of an original Colt Single Action Army revolver... the old topstrap had disappeared as a result of a reloading accident, along with the top half of the .45 Long Colt caliber cylinder...
I got the remains of the revolver as junk and used it as one of my first gunsmithing projects about 30 odd years ago. I hand filed/ground a piece of tool steel into an appropriate shape for a flattop and welded it into the space at the top of the revolver... then I machined the new strap to accept exactly the rear sight assembly shown in your photo. A new cylinder and 7.5 inch barrel in .38 special completed the mechanicals, and then it was color case hardened and blued... It was so pretty that it sold in less than a week to a regular customer who understood that no hi-velocity loads were to be used in it... wish I knew where that gun were now.
Anyway, the rear sight is definitely American made and likely added to a the stock Luger rear toggle by an enterprising gunsmith some time ago...
It should be a DANDY shooter!