These signs come in various different forms and have a range of intentions. Some are to warn drivers that their on board safety systems will be inoperable throughout a certain section of track or to provide a visual instruction to a driver that must be adhered to.
Found in a variety of different locations around the country, the distant board is effecively used as a distant signal and the reflective nature of the board allows inmproved visibility for drivers. These signs can be found with the arrow pointing either left or right, and can also be found with colour indicators placed underneath.
A fairly common site on the UK rail network, these signs tell a driver that an already received AWS indication can be ignored. Originally they were found in black on white or white on black configuration but were then replaced mostly by white on blue indicators as seen below.
In some station areas where the layout is considerably complicated and all lines are low speed, AWS may not be present and this sign indicates that no AWS is installed beyond that point.
Following on from the commencement sign above, this sign indicates that AWS equipment is installed beyond this point.
The sign informs that AWS equipment on the line beyond this sign and applicable to movements in the opposite direction has not been suppressed.
Following on from the sign above, this sign informs that normal AWS working resumes beyond the sign.
These signs are very common and varied and can be found in hundreds of locations around the country. They are designed to make the driver halt the train and follow the specific instruction noted on the board.