When the Prophet ﷺ intended to write to the Byzantines, it was said to him, "Those people do not read your letter unless it is stamped." So the Prophet ﷺ took a silver ring and got 'Muhammad, the Apostle of Allah' engraved on it .... as if I am now looking at its glitter in his hand.  

لَمَّا أَرَادَ النَّبِيُّ ﷺ أَنْ يَكْتُبَ إِلَى الرُّومِ قِيلَ لَهُ إِنَّهُمْ لَنْ يَقْرَءُوا كِتَابَكَ إِذَا لَمْ يَكُنْ مَخْتُومًا فَاتَّخَذَ خَاتَمًا مِنْ فِضَّةٍ وَنَقْشُهُ مُحَمَّدٌ رَسُولُ اللَّهِ فَكَأَنَّمَا أَنْظُرُ إِلَى بَيَاضِهِ فِي يَدِهِ