Help please! Lion and D in shield Hallmark?

Hi does anyone know what the D in a shield means? Also next to a lion?

This is a partial London hallmark with the lion passant for sterling silver and the date letter D for 1879. The missing parts of the hallmark are the uncrowned leopard’s head mark of the London Assay Office, a maker’s mark and (if duty were payable) the duty mark comprising Victoria’s head.

Partial hallmarks were used on composite items such as boxes where either the full hallmark or the missing components would have been applied to the other part. I note that there are 2 circular holes visible in your picture; is it part of a watch case?