When the Prophet ﷺ intended to write a letter to the ruler of the Byzantines, he was told that those people did not read any letter unless it was stamped with a seal. So, the Prophet ﷺ got a silver ring-- as if I were just looking at its white glitter on his hand ---- and stamped on it the expression "Muhammad, Apostle of Allah".  

سَمِعْتُ أَنَسًا ؓ يَقُولُ لَمَّا أَرَادَ النَّبِيُّ ﷺ أَنْ يَكْتُبَ إِلَى الرُّومِ قِيلَ لَهُ إِنَّهُمْ لاَ يَقْرَءُونَ كِتَابًا إِلاَّ أَنْ يَكُونَ مَخْتُومًا فَاتَّخَذَ خَاتَمًا مِنْ فِضَّةٍ فَكَأَنِّي أَنْظُرُ إِلَى بَيَاضِهِ فِي يَدِهِ وَنَقَشَ فِيهِ مُحَمَّدٌ رَسُولُ اللَّهِ  

Messenger of Allah ﷺ sent his letter to Khusrau and ordered his messenger to hand it over to the Governor of Bahrain who was to hand it over to Khusrau. So, when Khusrau read the letter he tore it. Saʿid bin Al- Musaiyab said, "The Prophet ﷺ then invoked Allah to disperse them with full dispersion, (destroy them (i.e. Khusrau and his followers) severely)".  

أَخْبَرَهُ أَنَّ رَسُولَ اللَّهِ ﷺ بَعَثَ بِكِتَابِهِ إِلَى كِسْرَى فَأَمَرَهُ أَنْ يَدْفَعَهُ إِلَى عَظِيمِ الْبَحْرَيْنِ يَدْفَعُهُ عَظِيمُ الْبَحْرَيْنِ إِلَى كِسْرَى فَلَمَّا قَرَأَهُ كِسْرَى خَرَّقَهُ فَحَسِبْتُ أَنَّ سَعِيدَ بْنَ الْمُسَيَّبِ قَالَ فَدَعَا عَلَيْهِمُ النَّبِيُّ ﷺ أَنْ يُمَزَّقُوا كُلَّ مُمَزَّقٍ