Were We Punked?

One of this life's bigger mysteries is how the people being punked during the first season of Ashton Kutcher's Punk'd! immediately knew they had been punked the second they spotted Kutcher. What the fuck? I can understand later seasons, after people had seen the show and were familiar with it, but nobody had seen the show at that point. How'd they know they'd been punked just because Kutcher showed up?