The Mark of the Prophet Is on His Shoulder

The Mahdi will have the sign of our Prophet (saas) on his shoulder.

(al-Haythami, Al-Qawl al-Mukhtasar, p. 41)

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

(Barzanji, Al-Isha'ah, p. 165; Al-Muttaqi al-Hindi, Al-Burhan fi Alamat al-Mahdi, p. 23)

The mark of the Prophet (saas) is on his shoulder.
(Barzanji, Al-Isha'ah, p. 163)

As can be seen from these hadiths, the Mahdi will have "the sign of the Prophet (saas)," an evident mark, between his shoulders. Islamic sources describe this mark as follows:

Jabir ibn Samura narrates:

The seal of the Messenger of Allah (saas) was the size of a pigeon's egg. (Tirmidhi)

Abdullah ibn Sarjis narrates:

I saw the seal of the Prophet (saas) between his shoulder blades, the left part covered with freckles reminiscent of warts. (Ibn Kathir, Shamail Rasul, p. 53)

Abu Saib ibn Yazid relates that: "My eye saw the seal of the Prophet (saas) between his shoulders."

(Sunan Tirmidhi, 6:126)

(He will have a mole shaped like a leaf on his shoulder blade)

Abu Basir quotes Imam Muhammad Baqir (as) or Ja'far as-Sadiq (as) (the uncertainty stems from the narrator) that he said: ... There will be a leaf below and to the left of his left shoulder blade, just like the leaf of the myrtle.

(Sheikh Muhammad bin Ibrahim Nomani, al-Ghaybah al-Nomani, p. 253)

Since a mole, referred to here as one whose edges are leaf-shaped, it appears the reference is to one that will be the color of skin, and that it is a mole with distinct edges and raised above the level of the skin, thus resembling a leaf in shape and of the color of a faded leaf.