The Tibetan Hair Ornament is the eighty-ninth treasure that can be found in Uncharted 2: Among Thieves.
The Tibetan Hair Ornament is found in Chapter 23 - Reunion. Once the threat is eliminated, you can find a treasure. This particular treasure is located atop a statue in the middle of this location. It's the statue closest to the stationary machinegun nest. The treasure is located on top of the statue's front end. Shoot it down from afar, and it will fall slightly. Then, climb up the back of the statue and work your way over its head so that you're sitting in front of its face. With the treasure shot down from afar, you can grab it easily from here.