One day, during a familly picknic, the ring was forgotten on a side of the towel and a raven, attracted by the shining gold, stole it. Ioan of Hunedoara managed to strike the raven with an arrow and got his ring back form the raven's beak. When this story was told at the royal court, the king decided to make the raven with the ring in the beak, the symbol of the royal familly. Also, the name of Corvin itself comes from the Latin "corvus" ("corb" in Romanian), which means "raven".
As any respectable Castles, this one has two a large number of legends and stories to tell but we advise you to discover them by going there.