It is narrated from Hazrat Anas (may Allah be pleased with him) that when the Prophet (peace and blessings of Allah be upon him) intended to write letters to the non-Arabs, the noble companions (may Allah be pleased with them) submitted that those people only read sealed letters. So the Prophet (peace and blessings of Allah be upon him) had a silver ring made. Its whiteness is still before my eyes. The inscription on it was: "Muhammad Rasul Allah (peace and blessings of Allah be upon him)."