Thanks for the pictures Mike & Ed.
The RANGELEY photo is particularly interesting as it shows a more common style of coat/hat hooks and no sign of rings of any kind above the windows or under the luggage racks.
So I am thinking, knowing the RANGELEY was built at a later time, during the "Franklin County Consolidation" when the lines came under MEC control, the rings are something more common to the mid-late 1800's that had passed from style by 1900 or so.
I believe an umbrella or cane-style walking stick would have been more common then, as more of a fashion statement as anything, and would hang easily from the rings shown. Also, a straight-stick style walking stick could be passed through one ring to rest atop the next ring either direction.
I'm trying to imagine what else would be common to the average traveler of the time the cars were built.
AHH!! I can think of one other item, and that would be a coat hanger! In the navy we had long garment bags for our uniforms with a space at the top for a hanger to protrude. In a sleeper accommodation there would be more room for such a bag, or just an extra suit-jacket to hang, perhaps in a small closet, but on a 2'er day-coach, what you see is what you get!
now, granted, hanging tour suit on one of those rings would obviously block your view out the window, but chances are your jacket would be considered more valuable than your view.
From the looks of the hooks provided for RANGELEY passengers, one could easily hang a hat, a suit, and an overcoat from the same hook and have a better view out the window. Time=experience=improvements.
Now, this is all speculation on my part, but there are now multiple identified common objects that could hang from such rings that have nothing to do with curtains or bells. So there ya' go.