Anas b. Malik reported that when Messenger of Allah ﷺ decided to write letters to the Byzantine (Emperor) they (his Companions) told him that they would not read a letter unless it is sealed. (Then) Messenger of Allah ﷺ had a silver ring made (for himself), (its shape is so vivid in my mind) as if I see its brightness in the band of Messenger of Allah ﷺ and its engravement was (Muhammad, Messenger of Allah).
لَمَّا أَرَادَ رَسُولُ اللَّهِ ﷺ أَنْ يَكْتُبَ إِلَى الرُّومِ قَالَ قَالُوا إِنَّهُمْ لاَ يَقْرَءُونَ كِتَابًا إِلاَّ مَخْتُومًا قَالَ فَاتَّخَذَ رَسُولُ اللَّهِ ﷺ خَاتَمًا مِنْ فِضَّةٍ كَأَنِّي أَنْظُرُ إِلَى بَيَاضِهِ فِي يَدِ رَسُولِ اللَّهِ ﷺ نَقْشُهُ مُحَمَّدٌ رَسُولُ اللَّهِ