The guidance (not legislation) is that lower case should always be used because all the evidence is that it’s easier to read for those who may have problems reading as the ascenders and descenders (I think these are the right terms) on the individual letters help some recognise the shape of words. I wish it was more rigorously enforced as at times we seem to have a hotch-potch of styles and fonts!Who decides if a station will be written as 'Cambridge South' or 'BRENT CROSS WEST' on the building exterior? I thought there were now recognised style guides on type faces, text sizes etc?
(I think upper and lower case is far neater FWIW).