If only one card had it, I'd assume it was just some weird surface scratch that got there somehow. But ALL of the cards I've ever looked at the backs of have those markings, so it wouldn't make me think something is wrong with it. I'd rather keep those little spots than that silly "DECKMASTER" label at the bottom of the card. I remember someone (Turgy?) pointing this out in an article. What is with that deckmaster thing, anyway?
I do have some cards from some white-bordered set (4th Edition, I think) that have this annoying print error where the inner frame of the card is pushed up so that the border is thin at the top and oversized at the bottom. This makes those cards easy to spot if you're playing without opaque sleeves and so way back in the day I noticed that the card sitting on top of my library was one of them and thought, "Lame. What am I supposed to do about that? Buy some of those expensive sleeves?" How young and foolish I was. Opaque sleeves were much cheaper back then than the prices I've seen more recently.
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