Narrated Anas bin Malik:When the Prophet (ﷺ) intended to write to the Byzantines, it was said to him, "Those people do not read your letter unless it is stamped." So the Prophet (ﷺ) took a silver ring and got 'Muhammad, the Apostle of Allah' engraved on it .... as if I am now looking at its glitter in his hand
Hadith No. 5875
Sahih al Bukhari