Trophy bones were the reward currency for the Crucible. You could buy the Supreme helm for 60 of them, and repair a set of Rogue gloves for 15 of them. With them, you could also buy taunts which was played for the player that you had defeated, and death titles that were applied to the foe you defeated.
Players could receive up to five trophy bones from the Crucible tutorials, one from each tutorial. Miles would prevent the player from picking up more.
After the release of Deathmatch, a convert option was added so that players can convert their trophy bones into deathmatch points at the rate of 50 points per bone.