The Sign Ring is a Magical Ring that Link acquires in Oracle of Seasons. There is no possible way to obtain the ring in Oracle of Ages directly but it can be obtained through a Linked Game by using the Ring Secret.
"100 signs broken"
In order to acquire this magic ring, Link will need to destroy 100 signs. Signs are found all throughout Holodrum and Subrosia. After destroying 100 of them, the Sign-Loving Subrosian will get angry and will flash a picture of the Nintendo and Capcom logos, making it appear as if the game suddenly restarted. The game will resume and Link will be given a Seed Ring as a badge of shame. This ring, when appraised, turns out to be the Sign Ring.
When worn, the Sign Ring has no effect at all. The purpose of this ring is simply to recognize that Link has destroyed 100 signs.