What if they found the tablets of the 10 commandments, signed by God, sitting out waiting for us to find? Imagine the panic. If God's existence could be proved, it would cause as much pandemonium as finding out that there's aliens on the moon watching our development. Which some believe to be true.
You couldn't prove it was God that signed it. Even if he showed up and said he did it then atheists or just any sort of doubtful person would question if it was really God. Even religious people would question if it was really God or the anti-Christ or some imposter.
For most people, people in authority have to declare the existence of something. So the newspaper and the President and some politicians would have to say what ever the strange phenomenon of any type was real. Even if aliens landed in your front yard and you had the best pictures in the world and they even stopped and posed with you and gave you a signed metal disc from the planet Zeist(composed of common metals even with an unexplained material), people would say the pictures are too good and you were a hoaxer or crazy.