The Messenger of Allah ﷺ wanted to write to the Romans, but he was told that they would not read any letter unless it was sealed. So he had a ring made of silver, and it is as if I can still see its whiteness on his hand. Engraved upon it was, "Muhammad, Messenger of Allah."
أخبرنا حميد بن مسعدة عن بشر وهو ابن المفضل قال حدثنا شعبة عن قتادة
أراد رسول الله ﷺ أن يكتب إلى الروم فقالوا إنهم لا يقرءون كتابا إلا مختوما فاتخذ خاتما من فضة كأني أنظر إلى بياضه في يده ونقش فيه محمد رسول الله
Bukhari transmitted it in the Book of Knowledge, in the chapter on what is mentioned about handing over books, and the chapter on scholars writing knowledge to different lands, hadith no. 65, and Muslim transmitted it in the Book of Clothing, in the chapter on the Prophet's taking a signet ring when he intended to write to the non-Arabs, hadith no. 56/2092, from the hadith of Shubah with this same chain, and it is also in Al-Kubra, hadith no. 9521.