It was found later at April Rose Antiques by Spencer and Jason after her disappearance. The anklet previously served as evidence in Alison's murder case until she was found alive and presumably returned to Alison.
In The Remains Of The "A"", Spencer and Hanna find a note planted by Garrett under Hilary Reynolds' hospital band for "A" with the name April Rose. Spencer later goes on a search with Jason to find out who "she" is. Jason later finds out that April Rose isn't a person - but an antique shop. Spencer and Jason get to the antique shop, and Spencer recognizes an anklet on a mannequin - it was Alison's. She had claimed that a 'friend' gave it to her, and she vowed to never take it off. Spencer takes it off the mannequin with her scarf to prevent smudging off any fingerprints. The shopkeeper says that it might have been brought there in the past few days, since he does not remember seeing it. Jason pays him $400 for the anklet.
Jason and Spencer hand the anklet over to the police, telling them they got an anonymous tip. Later, Mr. Hastings tells Spencer that important evidence in the Garrett Reynolds case (for the murders of Alison and Maya) was turned in last night, and he knows she turned it in. It turns out the police had been looking for the anklet for two years. Traces of blood were found on it - Alison's and someone else's. The blood did not belong to Garrett Reynolds and therefore cleared him of Alison's murder. It was revealed that Hanna's blood was on the anklet. The person who gave the anklet to Alison has not yet been identified, but it is possible that it was either Shana or CeCe.