question #1 Sahih al-Bukhari 2938, Book 56, Hadith 151 : What was the significance of using a seal on letters during the time of the Prophet Muhammad (ﷺ)?

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”.