this came with my shamisen a long time ago.
Very difficult to read for us modern Japanese. Some could read 貞助 (Sadasuke) which can be someone’s name that sounds very old, say some decades or hundreds years ago.Looks like possibly be Geisha’s name.I am not sure, though.
I cannot read other running Kanji letters.
Hope it can be any help.
Study hard, Cana(^_-)