The Messenger of Allah ﷺ wanted to write to some persian rulers. He was told that they would not read a letter without a seal in the form of a silver ring on which he engraved "Muhammad the Messenger of Allah."
أَرَادَ رَسُولُ اللَّهِ ﷺ أَنْ يَكْتُبَ إِلَى بَعْضِ الأَعَاجِمِ فَقِيلَ لَهُ إِنَّهُمْ لاَ يَقْرَءُونَ كِتَابًا إِلاَّ بِخَاتَمٍ فَاتَّخَذَ خَاتَمًا مِنْ فِضَّةٍ وَنَقَشَ فِيهِ مُحَمَّدٌ رَسُولُ اللَّهِ