PERISCOPE, MIOG ??

[xr7ator]

The only thing I can find is "Manual of Investigative Operations and Guidelines".

Did this just fall off of a purchase from a surplus store or what(zit)?

 

[nhbenz]

I think it's supposed to be M10G, which was used on some tanks.
Here's an M10 on which the tag seems to have modified to say M10D (upgraded from an earlier letter? Or did they run out of the right tags )
https://www.worthpoint.com/worthopedia/vintage-m10-tank-periscope-475977940