The "GFT" item, or Sagan Box, designed by the Sagan Institute at the request of the SGC as a hypothetical greeting from Earth, has been given as a gift to friendly races including the Cimmerians and the Tok'ra. It includes a representation of Earth and the various Earth cultures, religions, and histories. It also contains traces of iridium which will leave a recognizable nuclear signature that can be traced if it is sent through the stargate against a closed iris. The Sagan box was used by the Cimmerians and the Tok'ra as an early means of identifying contact by friendly races without risking opening the iris, but allies were later offered individual IDC codes for identification.
Cross Reference: Gairwyn, IDC, Iris, Kendra
Episode Reference: Thor's Hammer, Thor's Chariot, The Tok'ra, Serpent's Song