Amen Brother! So many want a sign, but by Faith alone are we to believe.
As for The Flood... I have not yet re-read the story (my wife and I are going through the New Testament but we would like to go back to the Old Testament once we wrap up the New Testament). But based on what we've read about Jesus, I am beginning to conclude that why should there have to be any scientific evidence that The Flood, as described in the Old Testament, occurred at all?
If with God, all things are possible, then surely He could cover the entire planet with water for 40 days and nights (how all that water would be present on the Earth would defy the laws of physics, as even if all the major ice caps and glaciers melted, there would still be land), drain it, clean things up, and leave no trace of the same. These things are completely impossible to do in a human or any scientific context. Scientific evidence of The Flood would another one of those signs that non-believers keep asking for.
Using science to "prove" the existence of God is pointless... we are taught that God cannot be seen by humans. I would think that our resources are better spent teaching the Gospel to people who are in need of salvation instead.