有序入场

The Guest Book can be found on the Astral Express

Could be a reference to the news article "Packed Onto Trains, Migrants Make Orderly Entrance Into Austria". Or, since the Astral Express is a train and Pom-Pom became a stricter conductor after what Aha did, perhaps Orderly Entrance is a new rule to ensure that guests/new passengers are thoroughly and orderly checked when they board and leave the Express.