1951 Mickey Mantle Signed Postcard, Rare Rookie Autograph Signature. Auto JSA1951 Mickey Mantle Signed Postcard, Rare Rookie Autograph Signature. Auto JSA If you're in search of an extraordinary Mickey Mantle rookie autograph, your search ends here. This is, without question, the finest example we've ever come acrossand also the largest! Measuring an impressive 3. 5 inches in length and nearly a full inch wide, its a true standout. Signed by "The Mick" himself just days after he became a professional baseball player, this