Until the 1970s or so, when the BMT, IND or IRT subways, or the successor umbrella agency, the Metropolitan Transit Authority, wished to highlight a museum, church, or service center at any subway station, there were a couple of different ways to accomplish the task.
There would be a large enamel sign, mounted on a wall or from the ceiling, listing the church, etc. with an arrow pointing to the closest exit. These signs were sometimes hand-lettered (expertly) and in the case of the IND, using their individual specialized typefont.
Sometimes, a signpainter would be hired to paint the lettering directly onto the wall, as in this sign for the now-defunct St. Vincent’s Hospital, at Greenwich Avenue and 7th Avenue South. (I have tacked a photo of a similar “To Toilets” sign on a wall outside my bathroom.)
Seen below the painted ad is the now standard issue MTA Unimark sign, which appears identical to its black and white directional sign, but with gray instead of black.