The Guard, known as a conductor in America, blows his whistle when it is time for trains to leave and sits in the brakevan (or a brake coach for passenger trains), where he can apply the brakes in case of an emergency. Guards also have two flags, one red and one green. The green flag means "all set" and the red flag means "danger" or "stop". They often tell the driver what to do.
A guard's uniform is blue pants, a white shirt, a black tie, with a blue jacket over them, and a blue cap with a black brim and brass plate.