I found 2 examples with nearly the same motif,both from Choshu Yaji-family Tomohisa,one from the Museum of Fine Arts-Boston,the2nd from an auction catalogue where this Tsuba was lot 540.Either "my" Yamashiro Tomosada took Tomohisa's motif or vice versa or there was a 3rd artist!?
Christian,I am sorry but I don't have Kuznitzky's Artibus Asiae "Han & Kakihan"
I am still hoping to get the meaning of the seal from an expert of our board.Ludolf