Any time you're on the clock and inside a park, you're on stage.
Inside the parks is considered on stage, outside the park is backstage, employees are cast members in costumes, customers are guests. All of this contributes to the Disney magic. Once you set foot on stage, you have to follow all the Disney rules and live up to the Disney image. This is also part of why there are tunnels under the Magic Kingdom — cast members shouldn't be seen outside their area because it hinders the experience. It doesn't make sense to see someone in a Frontierland costume walking across the park to Tomorrowland to meet up with a friend. Thus, the tunnels. But I promise, it's not as stressful as it may sound.