Our Prophet (saas) reveals in the hadiths that there will be certain distinguishing moles and marks on Hazrat Mahdi's (as) body

HIS [HAZRAT MAHDI’S (AS)] LEGS ARE WIDE AND STOCKY AND THERE IS A MARK THE OPPOSITE COLOR TO THAT OF HIS BODY ON HIS RIGHT LEG.

(Mu’jam al-Hadith al-Imam Mahdi Vol. 4 p. 154 and Kamal Ud-din Vol. 2 p. 376 and Bihar Vol. 52, p. 322)

THERE IS A BLACK MARK ON HIS (HAZRAT MAHDI’S (AS)) RIGHT LEG.

 (Sheikh Muhammad  ibn Ibrahim al-Nomani, Ghaybah al-Nomani, p. 251)

Humran ibn A'yansays: I asked Imam Muhammad Bakir: ...THERE IS A MARK ON HIS BROW, and a mole on his face.
(Sheik Muhammad ibn Ibrahim al-Nomani, Ghaybah al-Nomani p. 252)

Humran bin A'yânsays: to Imam Muhammad Bâkır: ... THERE IS A MARK ON HIS BROW, and his face is beautiful... "
(Sheikh Muhammad  ibn Ibrahim al-Nomani, Ghaybah al-Nomanip. 252-253)

Abu Basirsays: From Imam Muhammad Baqir or Jafar al-Sadiq. He said: "O Abu Muhammad! There are two portents (or signs) of the Qaim. THERE IS A MARK AND A MOLE ON HIS HEAD...
(Sheikh Muhammad  ibn Ibrahim al-Nomani, Ghaybah al-Nomani, p. 253)

Hazrat Mahdi (as) will have the sign of prophethood on his shoulder as the Prophet (saas) did.

(Al-Qawl al-Mukhtasar fi Alamat al-Mahdi al-Muntadhar, p. 41) 

The sign of the Prophet (saas) is on his shoulder.

The mark of the Prophet (saas) is on his shoulder.

 (Al-Barzanji, Al-Isha'ah li-ashrat al-sa'ah, p. 163)

…THERE IS A MARK RESEMBLING A LEAF BENEATH HIS (HAZRAT MAHDI’S (AS)) SHOULDERS.

(Mu’jam al-Hadith al-Imam Mahdi Vol. 3 p. 283, h.766)

 (Al-Muttaqi al-Hindi )

Hazrat Mahdi (as) has a thick beard, bright front teeth, a mole on his face, and a broad forehead.