Letter signed in blue ink by Casey Stengel on Aug. 13, 1963 on New York Mets letterhead. Stengel was manager of the Mets at the time and the first Mets manager. Note that the Mets at the time were still playing at the Polo Grounds. The letter is in near mint condition. See the 600 dpi high resolution scan. The signature has not been professionally authenticated but a comparison with authenticated Stengel signatures appears to be a clear match.