Stylized artist's signature ("AC") from the American sculptor best-remembered for his invention of the mobile and stabile, signed on a first day cover (without stamp) issued by the World Federation of United Nations Artists, featuring a design by Calder. The signature is slightly shaky, being executed shortly before his death, else in fine condition. 6.5 x 3.5 inches (16.5 x 9.2 cm). Together with the original transmittal envelope addressed to the collector and postmarked August 13, 1976.