Hazrat Mahdi (as) will be recognized by his dignity and majesty

Harris Ibn Mugaira al-Nasri says: Asked, “How will the Imam [Hazrat Mahdİ (as)] be known?” Imam Jaffari Sadiq answered:

BY HIS DIGNITY AND MAJESTY.

“How else will he be known?”

Also by what is lawful and unlawful, he will be known by PEOPLE’S NEED OF HIM AND HIS NEEDING NOBODY, and the weapon (sword) of the Messenger of Allah (saas) will be at his side.

Abu’l Jarud says: Asked how the imam [Hazrat Mahdi (as)] who will come after any qaim imam from the Ahl al-Bayt will be recognized, Imam Muhammad Baqr answered:

“BY HIS DIGNITY AND MAJESTY and by the acknowledgment of Ali Muhammad of his actions...

http://www.al-shia.org/html/tur/books/book1/021.htm#link20