The question of what Snow White’s engagement ring does is it leads the owner to true love. We saw in the season 1 finale that Rumpel had enchanted the ring so that it glows brightly when Prince Charming is close to his true love, Snow White. Now that magic has come to SB, I think that the ring is once more enchanted to lead the owner to true love.
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"That’s how you know you’ve really got a home. When you leave it, there’s this feeling that you can’t shake. You just miss it." Neal Cassidy