I've had this tanto for several years and continue to wonder about it. The omote is signed: "Uchi Mono Ume Tada Hiko Ichi", with a horimono of a tiger in the bamboo. On the Ura side it is simply signed, "Tada Hiro," with a carving of bamboo. Unusual format. The Tadahiro kanji doesn't match any specimen signatures that I have access to but there was a long line of this group & I have no idea if this is truly a genuine Mei of a lesser member or if it is simply gemei but on an uncommon side of the nakago?