In 1796, Congress authorized the creation of Seaman’s Protection Certificates as a way to prevent foreign navies from kidnapping or “impressing” American mariners into service. Issued by the US Customs House of the home port, the certificates were proof of American birth or citizenship including the name of the sailor, his age, height and other distinguishing physical features such as scars, birthmarks and hair color. One copy was held by the mariner and a duplicate was filed with the Custom House, now in the custody of the National Archives.
Seen here, a 1797 protection certificate for 15 year old John Borden signed by William Ellery, from the NHS archives.