There's no mistaking it - this hilt comes from a powerful, ancient weapon, but which one? I do not recall seeing or hearing of a sword with these markings, but that doesn't mean that all is lost.
Korialstrasz, better known as Krasus, has long been a friend to the quel'dorei and the Kirin Tor. With his vast knowledge and resources, he's certain to know something. Travel to the top of Wyrmrest Temple and seek his counsel, then report to Arcanist Tybalin inside the Silver Enclave in Dalaran.