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. (Using translation from Bukhārī 5875)
لَمَّا أَرَادَ رَسُولُ اللهِ ﷺ أَنْ يَكْتُبَ إِلَى الرُّومِ قِيلَ لَهُ إِنَّهُمْ لَنْ يَقْرَءُوا كِتَابَكَ إِذَا لَمْ يَكُنْ مَخْتُومًا فَاتَّخَذَ خَاتَمًا مِنْ فِضَّةٍ وَنَقَشَهُ مُحَمَّدٌ رَسُولُ اللهِ قَالَ أَنَسٌ فَكَأَنَّمَا أَنْظُرُ إِلَى بَيَاضِهِ فِي يَدِهِ