One, signed by Lincoln 23 days before his assassination, is a form appointing Lewis C. Gunn as a federal tax collector for California, the San Diego Union-Tribune reported. More than six decades later, Gunn's son-in-law, George C. Marston, founded the San Diego Historical Society.
The other document, dating from 1841 when Lincoln was a lawyer, is a debt-collection letter written on behalf of a client. The letter, while unsigned, is entirely in Lincoln's handwriting.
Jane Kenealy, an archivist at the center, discovered the framed appointment form in a box while she was going through some of the center's un-archived material. When she examined the signature, she remembered seeing the same handwriting on a letter.
Both documents go on display this week at the center.