For non-Christians: What would it take?

[Silver]

For those who are making the claims of a higher being appearing before you, do you mean before you alone or before the entire world? If you alone, how are the rest of us to know you are not merely delusional.

Taking the world wide route, if a higher being appeared before everyone, how are we to know it is indeed a God/dess? What if it was a highly evolved alien species with particular powers derived from higher brain functions?