I have never seen a pattern like this in a ceiling before. Looks like moisture with a hint of termitacitus. There is a furnace with ac coil in the attic (no drain pan). My first thought was moisture leaking onto the ceiling, but it does not look like a moisture stain (odd pattern and no staining on the drywall in the attic). Also thought about termites, but no sign of them anywhere the attic and no other signs anywhere else (this was found on the second floor ceiling in the center of the home). I am tring to figure this one out and can’t make sense of it. Any thoughts???