Why? “If you are wearing a head Phone, how can you hear the beneficial information via our Public Address system?”
Oddly, while I was taking this picture, someone came up to read the valuable ‘Service Information’ and read this. Lovely handwriting, but is this as important as the delays on the District, Circle, Central and Piccadilly lines? (But all other lines are operating a good service mind you.)
Of course, someone with a marker could be having a little fun with the ‘London Underground Tube System’ signs.