I noticed a Southern class 277 I think, with first class marked by a yellow line in the middle of the carriage. I've never seen that before?
There is a separate thread on this, under 377/6s. Briefly, Southern has finally decided to make the first class labelling on its 377/6 and 377/7s clearer by putting a yellow cant-rail stripe on and the words "first class" below the windows, after years of refusing to do so. About a third of the units now seem to have been done (with the usual inconsistencies to be expected from Southern!).