A comment here, on an article about same-sex marriage, amused me. As "proof" of God's existence, the commenter mentioned a lightning strike on the Vatican on the same day the Pope resigned, and added:
Now, in my life, I have never ever heard of the Vatican being struck by lightning. That, neanderthal, was a sign from God and not one of anger. Why wasn't it an act of anger as we are speaking of lightning? Because the bolt did no damage. That strike was a sign of God's love and approval of Benedict's strict adherence to Christian orthodoxy.
Out of curiosity, I looked it up, and yes, there is indeed a photo (thought to be genuine) of lightning striking St. Peter's Basilica that day. But if you read the article, you'll see that the photographer waited patiently for two hours through a thunderstorm, hoping that he might get a cool image. If you look at Wikipedia's images, you'll see that the Basilica "dominates the skyline of Rome"-- i.e., it's the tallest structure around. This means that in a thunderstorm, it's the most likely target for lightning. Admittedly this never seems to have been photographed before-- but that doesn't prove it's never happened before, but rather that no photographer has had the patience to wait before, or has been lucky enough before. It's an interesting coincidence that it hit on the same day that the Pope resigned, but of course we wouldn't have heard of it at all otherwise. The fact that it's gone viral is a good example of confirmation bias-- people want to believe God cares about the Pope, and therefore anything affecting the Vatican naturally must have to do with God. But if the Roman gods were still a competing religion, it could be seen as an expression of displeasure by Jupiter just as readily.
In short, this is a highly unconvincing argument for the existence of God. In any event, if the best way God can show his power is to strike the tallest structure around in the middle of a thunderstorm, he hardly seems to be worth bothering with.