The Motley Cap is one of Kefka's unlockable weapons. It can be obtained either by random chance when redeeming a Treasure token, or by purchasing them from the Shop for 7,200 Gil. Like all other characters' weapons, having it equipped carries no advantages or disadvantages.
A motley refers to the traditional outfit of a court jester, fool, or harlequin characters in commedia dell'arte, often appearing as a patchwork of red, green, and/or blue diamonds. In some cases, jingle bells are placed on the outfit. In some cases, they also wear a cap that has bells on it and at least two curved points, called cap and bells, that are designed to either refer to a donkey's ears, horns, or a cockscomb crest.