Apollo 15’s mission was the most dangerous due to the part of the moon they were landing on. Before leaving, they were to drive the Rover out to record the shuttle leaving the moon. The crew had smuggled a beautiful tin plaque onto the ship without NASA’s knowledge.
The plaque listed all the astronauts and cosmonauts that had lost their lives in furthering space exploration. They had a brief ceremony when they left the plaque and a small statue on the moon. That must be a record for longest 'art smuggling' distance ever.