Esto es lo que Vanity Fair asegura en su número especial Hollywood que se llama: “NUMBRE ONE IS WALKING” y viene a ser :

"meaning a film´s star is on his or her way to the set from the trailer. typically shouted by the A.D. (assitant director), based on the actor´s assigned number on the day´s "call sheet", (the schedule of scenes to be shot that also lists casts and crew arrival times on set). the lead actor are known as the "firs team" as opposed to their stand-ins, the "secondi team".

De Takeshi Kaneshiro Net