I am registered with the London Assay Office, at Goldsmiths' Hall (which is the origin of the term Hallmark).
I hallmark all solid gold pieces, even if they are under the weight that legally requires it (1g).
Silver pieces are hallmarked if legally required (7.78g and over).
I do not stamp any pieces with "925" (although some bought-in findings, like clasps, may carry this mark). It is NOT a legally recognised mark and is regularly abused.