The box contains information pertaining to the people of Earth, extending a hand of friendship, as well as iridium, a distinct nuclear signature Captain Samantha Carter had installed which would be detectable in the event the box was ever returned.
The box has been used several times with various races. Dr. Daniel Jackson gave the box to Kendra in hopes that Thor and his people will return to take it. Gairwyn later threw the box through the Cimmerian Stargate where it impacted Earth's iris, leaving a detectable iridium signature. (SG1: "Thor's Hammer", "Thor's Chariot")