That might have been an ad plane. When they're not directly overhead you can't see the message display very well. You just see the side of the display. Ad planes are rare these days. They were all over the place in the 70's. And they had a different design with bare light bulbs just hanging down from a wire frame, which made them much more noticeable from edge on. They spawned flying saucer reports galore.
Was there a stadium game or some other outdoor event nearby that it might have been circling over?