It should be a coupon that is obtainable from Adventure HELL chests and can also be bought from the Medal Shop and would basically turn timed Carat items from the Shop into permanent versions. For example; Cross Tattoo (Top), Taekkyeon Shorts (Bottom), Vicious Gloves (Gloves) and Huggs (Shoes) are all timed but their stats are garbage. For what reason are they timed? Who knows... ¯\_(ツ)_/¯