Quote from their website:
A website explaining the signs and signals relevant to train drivers on Britain’s national rail network, past and present.
.......learn about the many different signs and signals that appear by the side of Britain's mainline railways for the purpose of conveying information or instructions to train drivers. The object of this website is to illustrate, and explain the meaning of, every signal indication or lineside sign that exists today or has existed in the past. Never before has all this information, which includes historical details as well as modern regional variations and 'one offs', been brought together and made available from a single point of reference.