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I had the item signed at Spacefest this year. Mike Collins and Buzz Aldrin signed for the crew. The two other signatures are from two other Apollo astronauts who were CAPCOM (capsule communicators) for the mission. Charlie Duke (later LMP on Apollo 16) was CAPCOM during the landing, and added his famous, "We copy you down, Eagle!" This made Duke the first human to talk to a astronauts on another heavenly body.
Bruce McCandless II, who never flew on Apollo but later was the first person to fly untethered in space, was CAPCOM during the Moon walk. He inscribed, "Neil, we can see you coming down the ladder now," which he said just after the TV camera was turned on and Armstrong was descending to the lunar surface. McCandless became the first person to talk to someone standing on another heavenly body.