For fresher adhesive residue, use your thumb, create friction by pushing hard and rubbing glue residue towards closest edge. Clean thumb as needed and try again. Do you really want your slabs smelling like fish, peanut butter, nail polish remover, WD-40, etc? Slabs are so easy to scratch, I wouldn't use any cloth or paper towel.
The kind of stickers I'm removing are ~15 years old and not coming off with a thumb. Some barely come off with WD40 / GooGone and a lot of work with q-tips. The smell is a downside, and is the reason I mostly stopped using WD40. Cleaning up the slab with a dab of soapy water after Goo Gone helps with the citrus smell. Here is one I did manage to cleanup nice. Seller before: Mine after: