When the Messenger of Allah ﷺ intended to write to the Romans, it was said to him, "They do not read any letter unless it is sealed."So the Messenger of Allah ﷺ had a ring made of silver. It is as if I can still see its whiteness on the hand of the Messenger of Allah ﷺ. Its inscription read, "Muhammad, Messenger of Allah ﷺ."
لما أراد رسول الله ﷺ أن يكتب إلى الروم، قال: قالوا: إنهم لا يقرؤون كتابا إلا مختوما قال: فاتخذ رسول الله ﷺ خاتما من فضة كأني أنظر إلى بياضه في يد رسول الله ﷺ، نقشه محمد رسول الله ﷺ.
Bukhari reported it in jihad (2938) and in dress (5875), and Muslim in dress (56:2092), both of them by way of Shuba, who said, I heard Qatada narrating from Anas bin Malik, who said, then he mentioned it. It came with the wording, "when he intended to write to the non-Arabs," and with the wording, "to Khosrow, Caesar, and the Negus."