Thanks for confirmation - never seen that before. Why does each set have a different letter then? Is that necessary?
To be fair, I've not seen it before either and certainly seems to be a recent addition as the letters weren't there when the 442s left swt 10+ years ago.
It seems the PIS (Passenger Information System) screens inside each carriage aren't capable of displaying the coach number, unlike swr desiros which had the faculty added.
Often when people board they don't know what carriage they are in and people being in the wrong part of the train at short platforms is still a problem. At least with the desiros, when the guard says you need to bein the front 5 for the next station, people can refer to the screen and see they are in coach 7 and need to move forward.
The 2105 Waterloo to Poole which is supposed to be a 442 eventually, will stop at a number of stations which are short platforms. We'll have to wait and see how effective the lettering system is, but it seems to be a good idea if the PIS isn't capable of displaying it.