The Apollo astronauts all wore Omega Speedmasters to the Moon, but when they came back, all of them became property of NASA all over again, which then disseminated them to archives and museums the world over. But Apollo 17 astronaut Ron Evans attached one to a heat flow engineering experiment, different from the one he wore on his wrist. That watch wasn't handed over at the end of the mission – and it's the only Speedmaster in private hands. And it's .
On December 15, 2015, Christie's will auction off the watch. No opening bid has been announced, but the last time it was up for sale in 2009, it went for $23,900, according to . It's going up alongside the wrist strap from the watch Evans wore and the pen he used on that mission, the final one to visit the moon.
Quick caveat: Evans was the Lunar Command Module pilot, meaning that while Harrison Schmitt and Eugene Cernan explored the lunar surface, Evans remained in orbit around the moon, awaiting their return while running a variety of experiments. Thus, it has been around the moon, but never to the surface. But regardless, there aren't a lot of watches out there for which you can say "this watch has been in lunar orbit before" unless you're one of those terrible people who stole them from some poor museum or archive.