Fans of Ugo Rondinone’s cheekily exuberant “Hell Yes!†sign on the front of the New Museum can breathe a sigh of relief — we’ve learned that the colorful work, which has adorned the building since it opened on the Bowery in 2007, won’t be coming down next month as planned. Originally loaned for a two-year exhibition, the piece was recently purchased for the museum by a group of image-conscious trustees. It will now remain up for at least another year, “as it has become an iconic part of the New Museum’s branding,†says spokeswoman Gabriel Einsohn. Clearly the museum’s leadership has picked up a lesson or two from the gen-Y-ers in its “Younger than Jesus†show, which closes tonight July 5: In today’s uprooted, multi-platform art world, it’s all about the brand.