The Prophet ﷺ used to wear the signet-ring on his left hand, and put its stone next the palm of his hand. Abu Dawud said: Ibn Ishaq and Usamah b. Zaid transmitted from Nafi': "On his right hand".
أَنَّ النَّبِيَّ ﷺ كَانَ يَتَخَتَّمُ فِي يَسَارِهِ وَكَانَ فَصُّهُ فِي بَاطِنِ كَفِّهِ