Ans: 1) Warner signal - When in 'on' position, it indicates that the signal ahead is at danger and driver must be prepared to stop at next signal. When in ‘off’ position it indicates that the signal ahead is in proceed position and driver can take the train speed. It is the first signal for train entering the station.
2) Co-acting signals- Where due to obstruction such as over bridge, arm or light of main signal does not remain in the view of driver, during whole time co-acting signals are provided. They are fixed below the main signal.
3) Shunt signal - For controlling the shunting operations in the station yards shunt signals are used. They are mounted about 0.5m above ground or fixed on same post as departure signal.
4) Detonating signals- Are used in foggy weather to indicate the locality of a signal to the driver of approaching train. These are placed on the rails and explode when engine passes over them.