Actually, this is Ellen's swinging pad.
First 100 lb cover stock and binder's board is cut into 2-1/2 x 2-1/2" squares.
The corners get rounded, including the boards.
I mix watercolor with PVA. In this case it's Dr. Marten's watercolor. There is actual "padding adhesive" on the market---but it just seems like watered-down PVA. And with paper this heavy I think you need a fairly beefy adhesive.
Spines get glued out under pressure. If these were any bigger, I'd have them on their sides, on the edge of the bench with a heavy weight on top. But these are small enough for the press. And they stay in the press or under weight until dry.
And there it is: Ellen's amazing tag pad. You just peel off a tag whenever!
There's actually two versions; the other has the hole drilled in the corner. It's very stylish and I wish I'd taken a picture of it.