Sake cup signature translation

It appears to be Japanese blue and white brush style signature, on what also appears to be a single sake cup. I could be entirely wrong. I've searched for hours through loads of different websites, google image searched it, asked others to search, etc and we cannot find the same signature anywhere. Is this an anomaly? Is it not Japanese? Any help greatly appreciated.

https://imgur.com/gallery/WeqATdU

Because the letters are broken (cursive style?), I am Japanese, but I don't know for sure, but I thought it was 肇（Hajime ）(a name given to men) or 松尾 (Matsuo) (family name).
In the case of Matsuo, it looks like two letters are written vertically.

Thank you very much for your input!