Thanks for the japanese bronze translation. I think it may be a "mark" (like jun-gin, pure silver) rather than a signature. I googled what you gave me and found these on a Japanese Antique Glossary:

Dai-mei
A sword smith student signing the name of his teacher onto a blade forged by the student. A not uncommon (or unethical) practice in old Japan. (Samurai turned to other forms of metal work when samurai were banned.)

Sentoku (unique japanese bronze mix)
Alloy of copper, tin and zinc. Usually yellow or dark brown in color (which would account for the color of the vase.