The Pharisee's were like "Prove it, Mr. Big Stuff". All he could do was shake it head, I mean look at the situation. Jesus was THERE WITH THEM and they were still blinded, hearts were still hardened. More signs weren't gonna change a thing.
Where's the proof? That's the cry of the atheist. I can't see it so I don't believe it. I guess they've never read Hebrews, "...the assurance of things hoped for, the conviction of things not seen.", and all that. Like the Pharisee's, I believe the non-believer could be hit over the head with the most, well, miraculous miracle and still not believe. It comes from the heart and soul. The mind just gets in the way.
Father, let my little bit of love be a light for those who are too smart for their own good. I used to be one of them.