I took this photo in a small hallway at the foot of a stairwell; I wouldn’t be surprised if the hallway didn’t have a strobe prior to this unit being installed. Every other horn I saw in this building was mounted on a trim plate, while every Select-A-Strobe was mounted directly on the wall or ceiling; given the traces around the horn, it seems that the trim plate in this photo was perhaps originally in the horn’s spot and was moved when the strobe was added.
I was wondering the same thing about the original signals—I’m baffled as to what they may have been. For a 6500 from this era, I would expect 439D bells or 881D/885D Adaptahorns. However, the trim plates don’t look like an Edwards product; they’re not from an 881D (as they don’t have screws in the outer corners), and I’ve never seen 439Ds paired with trim plates (likely because these bells were already equipped with universal mounting plates and had fairly large bases that could cover imperfections).