Then Harry took off his left shoe, and his left sock, and took off the toe-ring that was Hermione Granger, the Transfigured shape identical to the toe-ring that had been given Harry as an emergency portkey.

(Chapter 111)

"Dumbledore resumed his examination. Harry had to remove his left shoe, and take off the toe-ring that was his emergency portkey if someone kidnapped him and took him outside the wards of Hogwarts (and didn't put up anti-Apparition, anti-portkey, anti-phoenix, and anti-time-looping wards, which Severus had warned Harry that any inner-circle Death Eater would certainly do). It was verified that the magic radiating from the toe-ring was indeed the magic of a portkey, and not the magic of a Transfiguration. The rest of Harry was deemed clear."

(Chapter 94)