A great hunting arrow, and a symbol of Apollo, Lord of Kobol.
Legend states that the Arrow is the one surviving clue to location of the planet Earth (Kobol's Last Gleaming, Part II). According to accounts of the scriptures of Pythia and Laura Roslin's statement to the Quorum of Twelve, the arrow is a key of sorts, which will open the Tomb of Athena. (Fragged)
This arrow itself, or an accurate facsimile thereof, was on display in the Museum of the Colonial Arts in the City of Delphi on Caprica (Kobol's Last Gleaming, Part II).
While the city itself suffered extensive damage as a result of bombing during the Cylon attack, the Arrow itself survived undamaged. It becomes the focal point of Laura Roslin's attempts to discover the whereabouts of Earth following the apparently accidental discovery of Kobol by the Colonial fleet (Kobol's Last Gleaming, Part I. These attempts lead to Lieutenant Kara Thrace disobeying orders and taking a captured Cylon Raider to Caprica, when the Raider is required in a plan to rescue personnel from the Galactica who have been shot down by Cylons over Kobol (Kobol's Last Gleaming, Part I).
It was housed in the Delphi Museum of the Colonies until collected by Starbuck and taken to the Astral Queen and Laura Roslin (Home).
It appears that the Arrow may actually be a true arrow that works as a mechanism with a bow found in the Tomb of Athena (Home, Part II).