Different Types of Signals: 1) Flag signals: This is shown by signalman if green flag is raised; it means to proceed with caution. Green flag shown down, it means there is track defect; the train should not go ahead. 2) Denoting signals: These signals are used in foggy / cloudy weathers to indicate the positions of a signal to the drivers of approaching locomotive. They are placed across the tracks and explode when the engine pass over them, which makes aloud sound and attracts the attention of driver. 3) Warner signals: ‘ON‟ position indicates the signal ahead is at danger and driver can pass signal with caution and be prepared to stop at the next signal. „OFF‟ position indicates A signal ahead is to proceed position and driver can take the train at speed. 4) Fixed Signals: Each section (or block section as it is often called) is protected by a fixed signal placed at its entrance for display to the driver of an approaching train. If the section is clear, e.g. there is no train in it, the signal will show a “Proceed” indication. If, however, the section is occupied by a train, the signal will show a “Stop” indication, usually a red aspect. 5) Two-aspect colour-light signals: In this, each signal has two lamps (one above the other). The higher of the two is a green lamp, and the lower one is a red lamp. The green lamp when lit indicates clear (the proceed indication), and when the red lamp is used for STOP indication. 6) Three-aspect colour-light signals: – In this, each signal has three lamps arranged vertically. The top one is green, the middle one yellow, and the bottom one is red. The red and green lamps indicate indications as in the 2-aspect system, and the yellow lamp shows the caution indication.