original signed box; creator-signed box
Refers to the original wooden box in which a piece of art (especially ceramics) is stored, bearing the artist's signature and seal. Used in contexts of art authentication and appraisal.
This tea bowl comes with its original signed box, so it is highly valued.
Having the original signed box helps determine the authenticity of the work.
Compound of 共 (とも, 'together with') and 箱 (はこ, 'box'), literally 'accompanying box'. The reading ともばこ is a rendaku form.