This United States one dollar bill holds the signatures of the three Apollo 12 astronauts (Charles "Pete" Conrad, Jr.; Alan Bean; and Richard "Dick" Gordon Jr.), all on the front of the bill. This memento of the second human landing on the Moon in November 1969 was part of the official process of certifying the flight.
Before human spaceflights, the National Aeronautic Association (NAA) had the astronauts autograph dollar bills, witnessed by the NAA official for the flight (who sometimes also signed the bill, but in this case did not). The bills were then placed aboard the spacecraft. After the mission, recovering the identifiable bills served "as the basis for certification of the identity of the astronauts on each of the flights."
The NASA Johnson Space Center transferred this bill to the National Air and Space Museum in 1976.