In some european symbolism the circle stands for God, so maybe it 's Turgons piety? In heraldry they are known as rings, roundels or annulets... i don't know what they stand for... i suggest they stand for signet ring and so symbolize lordship and vassalry. Though roundels may also symbolize fruits, apples for example... again modt likely a religious biblical symbolism.
I guess we may very well use a circle instead of a heart if we do not wish to recycle the heart epis8de (tjough i would be open to do so... but its not necessary )