I apologize for my crap cell phone pic. The first photo shows a knife lifting up the second membrane, exposing bare bone. This is very hard to remove so most give up even trying, if you do you will have a full rack of shiners, so don't do it. The confusion may come when you get a slab that for some reason the top membrane has been remove and you may try to remove the second one thinking it is the top one. Look close at the first bone with the knife and the edge of the second bone, you will see a little bit of what is bare bone and what the whole rib section would look like if it were removed.
The second photo shows the top membrane being pulled off by the paper towel this is what most of us pull off. Shiners show up sometimes if the second tuff membrane is damaged or cut usually by the butcher processing the ribs. This later opens up when cooking shrinks it and exposes the bone. As I said, putting a rub on the backside will not do much except flavor the meat above the bones showing and make the membrane taste better I guess. For the purpose of seasoning the meat above the bones I do season the backside, but leave both membranes on.