The Cullen Crest is a detail added in the film that doesn't appear in the books. Every member of the Cullens wears it on some sort of jewelery. It shows an arrow, three shamrocks, a lion, and a hand above the lion. If you are wondering about the meaning or the need of such a crest - stop right now, because this is Twilight. If something is shiny and beautiful and cool, it doesn't need any meaning or explanation!
The Cullen Crest

Yeah, this is what it looks like. Seriously, they had to do this?

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