Before purchasing a Ken Griffey very recently I was studying his signature for a couple of months or so. At first glance it looks like it has authentic characteristics but I haven't seen any of his signatures where the "n" in Ken attaches to the J like that; everything else looks good It could be authentic in my opinion; but if it was me, I'd only purchase it if I trusted the seller.
However, I've really only looked at signed baseballs. Is there a way you could get a clearer scan of the close-up image?
I would avoid this one. Mike's observation is right on. one other thing to consider, the relative height of the G vs the K here is not typical. the G is normally the highest point in the signature.