YEP! I have contacted them to request they don't put one on anything I buy. They are no guarantees they say.
When did they start doing this?
I have bought a ton of slabs from them, and not one has ever had a Comiclink sticker on it.
I don't know, it's been going on for quite a while, a year at LEAST. I personally have only gotten one slab (WD #6) with one of the stickers.
Like Phil say's, it's not really a huge deal, I don't mind it and knew it was there before I bought it, some people might be turned off by it. So long as it doesn't cover up any of the book I don't mind.