Xenophilius Lovegood's necklace was an ornament that he wore to Bill Weasley and Fleur Delacour's wedding. Some, like Viktor Krum suspected him of being a Dark Wizard, but actually the necklace simply bears the symbol of the Deathly Hallows to show that he believed in them and was used as a symbol to recognise other seekers of the Deathly Hallows.