I can't exactly see why seeing the mystery woman to be Sakura would be surprising to most people. from what I hear alot of people in Japan already consider NS canon, weren't there some advertisements that referred to Sakura as "Sakura Uzumaki"?
I think @Pepsi is talking about these stickers:

It's written Uzumaki Sakura on it.
Unfortunately, it's only fanmade. I think they were given at a convention about RTN, not very sure about it, but it's just fanmade. Otherwise, they would't be any debate on Naruto's end pairing anymore LOL.