Yeah, I was talking about the preview sleeves for the display cards, because if you are flipping through and there is a card on ever print (that wants on) in the bottom corner or something, you know exactly who made that when you look through, and if there is a place to stack cards you already know what it looks like, so it should be quick and easy to find it. Not that all your cards would be in one sleeve if thats what you were thinking, that would be a little chaotic XD Just one as an identifier, and one on all the actual prints.
The cards on the actual prints wouldn't need to be sleeved unless you wanted them to be. Any size can be worthy of a paper clipped bookmark, I dont think you would have to be worried about them sliding off or anything like that, you underestimate the power of the paperclip XD
It was just an idea, something I personally would do if I had prints and wasn't there to represent myself, Id want to make sure that every one who bought something has a way to contact me for anything.