Silver coin proof sets usually include certificates of authenticity. Silver jewelry is usually stamped with a number, such as 995 or 999, referring to parts of silver per 1000. Silver bullion or ounces of silver come with a proof of chemical assay.
A chemical assay can replace a certificate of authenticity and is generally considered to be a more accurate proof of silver content. Titration assaying is typically used to assay silver, but dry assaying and fire assaying are also used. At the same time, a certificate of authenticity provides additional detail such as the purity, the makers mark and a stamp of approval.