I'm sceptical, because from what I have seen from her lately, she doesn't really do this smiley-thing there infront of her "S.." anymore. And the signed photos are all quite new Divergent photos (meaning they can't be like two years old from when she signed that way.. although I don't know when exactly she stopped signing similar to that).
Her signature varies quite a lot, even at the same premiere you can get two autographs that look quite different from her. But I have never seen this thing at the beginning of her signature in recent signatures. As I said, she once did sign like that, but from what I've heard/seen her signature looked different recently.
Here are some examples for signatures of her from this year to compare to:
A possibility I see for the autographs you linked above to maybe be authentic are maybe only if they are a bit older, from last year, before she started promoting Divergent, but when the Divergent photos were already released. But I would rather tend to saying they are not.
But that's just my opinion, I'm no real expert when it comes to her signature, and of course just the fact that I haven't heard of her signing like that in quite some time doesn't guarantee that she hasn't.
The big question I would have is, when and where does the person who sells those autographs say that he/she got them?
