If the skies errupted with the sound of trumpets and an angel descended to tell me to do something, my first thought would probably be that I'm having some sort of mental break, but if the person standing next me is seeing it, too, then I'll be the first one carving some commandments or whatever. There's a perfectly achievable standard of proof for you.
Isn't the Atheistic position that there is a rational, scientific explanation for everything? Thus we don't need to reach the realm of divine?
This basically eliminates any occurrences of God, Angels and so on.
What I'm trying to say is this: if you can scientifically proof the existence of supernatural , then by logic there's no such thing as supernatural.