It appears from the information provided in the hadith that Hazrat Mahdi (as) will use the seal of our Prophet (saas) in his works and in everything auspicious, excellent and useful that he does.
It also appears from the hadith that Hazrat Mahdi(as) will use the seal of the Prophet (saas) in the works he writes or has prepared, and that he will adorn his works with the seal of the Prophet (saas).
It is particularly noted in this hadith that this seal will be golden, in other words, that a gold-colored seal will be used.
Jaffar Sadiq says: “It is as if I literally see Qaim [Hazrat Mahdi (as)]. HE WILL TAKE THE SEAL OF THE PROPHET’S (SAAS) GOLD-SEALED agreement OUT OF HIS POCKET and READ ALOUD to people."
(Bihar al-Anwar, Vol. 52, p. 326)