 In 2002 the 666 address on the side of the building was replaced with a Citigroup logo after Citigroup became the building's largest tenant.Citi occupied six floors totaling in the building due to its proximity to the company's headquarters at 399 Park Avenue.Although similar signage normally wouldn't be allowed in Manhattan, the signage on 666 Fifth Avenue was permitted under a grandfather clause since the original 666 signage was erected before the ban was enacted.