Today I purchased this sight from a Korean War Army veteran that told me that his friend, who had been in the pacific in WW2, gave him this sight and told him that it was from a Japanese artillery gun.
Also in the same day I got that type 90 helmet in the background like in this post->Sweet craigslist helmet find
It seems that whatever symbol was defaced, maybe similar to the chrysanthemum on Arisaka rifles? Anyway even if it weren't ww2, I still got a cool periscope for 40 bucks. Shed some light please!