Ester 8:2

8:2 The king then removed his signet ring (the very one he had taken back from Haman) and gave it to Mordecai. And Esther designated Mordecai to be in charge of Haman’s estate.

Ester 8:8

8:8 Now you write in the king’s name whatever in your opinion is appropriate concerning the Jews and seal it with the king’s signet ring. Any decree that is written in the king’s name and sealed with the king’s signet ring cannot be rescinded.