Japanese sign on Type 92 clip

I have a Japanese loading clip for the Type 92 machine gun.
This one has this mark on it. Is that a manufacturer’s mark or an arsenal mark.

It is a Japanese writing character “mu”, it is present on most Japanese chargers and magazines. I have no clue of what it means. Look here in the middle of the page https://en.wikipedia.org/wiki/Mu_(kana) to see how “mu” is written.
I personally look for “mu” to authenticate chargers as Japanese, because Chinese also made them post 1945 but without “mu”.

Thank you.