How a Young Fashion Designer Got Cannes Lions Buzzing With This Mysterious Dress

At the frenzied festival, Lilli Jahilo cut through the clutter

CANNES, France—When thousands of marketers descend on Cannes, the resulting chaos of banners, displays and branded freebies can overwhelm the senses. Which might be why one of the most effective posters at this year's Cannes Lions was the most simple and enigmatic.