Got told that it is for the stewards when it turns red theu are on alert to a serious crowd trouble problem
I don’t know the answer for sure, as I don’t think it was there when I was stewarding. However I don’t go along with the notification for stewards line as most stewards wouldn’t see it, and it’s in a very inaccessible place. There are other coded messages that alert stewards to situations, and senior stewards are in radio contact with the control room, so a light up on the gantry is unlikely to be the solution to situation management.
More mundanely, that used to be (and maybe still is) where the club’s video camera was placed when we didn’t have blanket TV coverage, and I suspect it may just be the club’s own video equipment, or part of the press facilities. It is the broadcast media gantry.