The Guard, known as a Conductor in the US, blows his whistle when it is time for trains to leave and sits in the brake van for goods trains or the 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 drivers what to do.
A North Western Railway guard's uniform consists of blue trousers, a black tie, a white shirt with a long blue overcoat, and a blue cap. Guards on the Skarloey Railway wear the same uniform in a blue-grey colour.
- A miniature model of a guard is now on display at the Hara Model Railway Museum.
- James' guard that appears in the first series episode, James and the Coaches, looks like Ringo Starr.