A Glamour Charm is an enchanted necklace that alters the physical appearance and voice of the wearer to create an illusion to the outside world. The charm is only effective while it is being worn.
Having worn the charm for weeks, Tigress had started the question her own intentions. She had built a life with Wally, but she threw it away in a heartbeat when Nightwing requested that she embark on the undercover mission. To the outside world, she was Tigress, a professional assassin, thanks to the Glamour Charm. The illusion was now in danger of becoming a reality, since Artemis was starting to forget who she was, and embrace her new life as Tigress.
While attending the summit between the Reach and the Light, Ra's al Ghul recognised Tigress's amulet as a Glamour Charm. He removed it, causing her to be seen for who she really was, not only blowing her cover, but Aqualad's as well.