The Wind Chime is a small bell you throw to lure one guard away from his post. It deals no damage on its own, but it is the cleanest way to split a single enemy off for a quiet kill.
Select Throw with L2 and left on the d-pad, equip the chime with L2 and Square, then throw with L2 and R2. The highlighted guard walks over to check the sound.
Throw it near cover so the guard walks into an assassination. Pair it with the Charm of Toxic Demise and it becomes a silent kill on its own.