The Houghton Library of Modern Books and Manuscripts at Harvard University has recently been given a Masonic membership certificate, signed by Prince Hall himself. The very rare certificate came from Harvard's W.E.B. Du Bois Institute, and is dated June 13, 1799. It is in the name of Richard P.G. Wright, and signed by Prince Hall (Worshipful Master), George Medallion (Senior Warden), Jube Hill (Junior Warden) and William Smith (Secretary).
Reproduction of the certificate is restricted and must be licensed by the Library. A detailed image of it can be seen here.