"Ring" in the Bible: Esther 8:2-10
The signet ring of a king acted as his seal of approval. The object itself has no power, much like a marriage ring, but it's a symbolically powerful item. In this passage in Esther, we see that any document sealed with the king's signet ring was as good as the king's word itself.
http://biblegateway.com/passage/?search=Esth.8.2-Esth.8.10&version=NIV