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." (Using translation from Abū Dāʾūd 4214)
أَنَّ رَسُولَ اللهِ ﷺ أَرَادَ أَنْ يَكْتُبَ إِلَى الْأَعَاجِمِ فَقِيلَ إِنَّهُمْ لَا يَقْبَلُونَ كِتَابًا إِلَّا بِنَقْشٍ فَاتَّخَذَ رَسُولُ اللهِ ﷺ خَاتَمًا مِنْ فِضَّةٍ وَنَقَشَ فِيهِ مُحَمَّدٌ رَسُولُ اللهِ