Elsewhere in New York, Showtime Networks has erected what it's calling the world's longest ad. It's the first ad to be mounted on the Port Authority building. The 10,350-square-foot, blocklong board is part of the cable operation's new $40 million "No limits" brand campaign. The ad was created by Red Group, Showtime's new in-house agency. Art directors: Ann-Marie Gillian, Nancy Mazzei.