Home Box

Home Boxes were present on Galaxy Class starliners of the 51st century. They were described by the Doctor as being like Black Boxes on airplanes. When something went wrong on one of these ships, the Home Box was somehow ejected and returned to the home planet with all the flight details.

River Song graffitied High Gallifreyan onto the Home Box of the Byzantium to contact the Doctor, knowing he would one day find it in a museum. Translated into English, it said "Hello Sweetie". (DW: The Time of Angels)