Those wandering the New York City streets on Monday may have been given the surprise of their lives: actress Alicia Silverstone's naked butt at the corner of 40th Street and 8th Avenue.In an ad for PETA, the 40-year-old actresses poses completely nude with her back facing the city streets in protest of sheep's wool.To really drive that point him, the iconic Clueless star delicately holds a sheep mask while the ad itself, photographed by Brian Bowen Smith, is emblazoned with the words "I'd rather go naked than wear wool." This is followed by "Wear your own skin. Let animals keep theirs.” Silverstone has been openly vegan for some time now, and while People reports that she had already nixed leather and down from her wardrobe, wool is the next step she's taking to ensure all animals' rights are protected.The often controversial animal rights organization, PETA, is behind the new Times Square billboard, and also featured Silverstone in a video on their site that goes deeper into what the campaign is really about."They’re cut. They’re harmed,” the actress explains. "They get very seriously wounded and there’s no care for them when they’re wounded. It’s just move on to the next. These are not creatures to the people who are doing this. They’re just objects. When the sheep are no longer useful, they’re killed. There is no happy place they get to go for being a wool sheep.”Suddenly we're thinking twice about those cozy holiday sweaters.