The short answer: Ga-something, Chin-something.
The long answer:
I suspect this is a four character mark. Reading top to bottom, right to left, the first character when read on its own is Miyabi (窶ーテォ). But this would be part of a two-character combination, and so the reading changes to ツ“Gaツ”. The second character directly under it would form the second part of the name, but it has been mostly eliminated by the hole in the item. The tiny bit that is left almost looks like the character Ryu (窶板ョ), which would make the name/mark ツ“Garyuツ”. I searched the web for a ツ“Garyuツ” mark but nothing turned up.
The third character (top left) is Chin (窶卍ソ). The character under this is indecipherable to me. It looks like a scribble. Since the other two characters are so carefully drawn, one wonders why this last character is so poorly rendered. Is it obscured by a stain, is it an effect of the photograph, is there a crack that has disfigured the character? Or, is it just a sloppy letter? Or could it be a counterfeit?
The two legible characters are fairly distinctive, and one would think that even with the other two characters being illegible something would show up in a search for Imari + Ga + Chin, or Imari + Garyu, etcツ…, but I couldn’t find anything.
Sorry I couldn’t be any more help.