I don't know about useless .... in isolation that is rather silly ... but I would hate to have a metal sign at head hight or lower that I ( or a child ) might run into because it was not lit up.
So the answer is light it up.... or fasten it to a wall.
If it is fastened to a wall ( or even if it is on a lit pole , how does the blind person know where the sign is anyway?
How can the sign be consistently located at the "similar" location at each station when each station is structurally different?
would be better off with a "station name" voice recording every 3 minutes or so
