An actual proof would require the supernatural being in question be very precisely defined. It would be difficult to define any physical being that precisely. But if we lower the standards from "proof" to "evidence so overwhelming that no reasonable person could dispute the conclusion", it becomes much easier.

For a god, especially a nigh-omnipotent, universe-creating god, the trick is to think big.

The WMAP mission measured the temperature of the cosmic microwave background radiation across the entire sky. This temperature was, in turn, directly determined by the location and density of all the matter in the universe during its very early stages (approximately 370,000 years after the big bang).

Now suppose that the WMAP data contained an artist's signature.

Any being that signed the early universe would have changed the nature of huge parts of modern universe as a necessary side-effect of putting the signature in place. And if they signed it later, they would have needed to modify a volume of space billions of light-years in diameter. Either way, that being is more powerful than anything humanity could ever hope to even approach. It is definitely worthy of the label "god". (We haven't actually proven that it created the universe, but if it claims to have done so, I'm not going to argue.)

An actual proof would require the supernatural being in question be very precisely defined. It would be difficult to define any physical being that precisely. But if we lower the standards from "proof" to "evidence so overwhelming that no reasonable person could dispute the conclusion", it becomes much easier.

For a god, especially a nigh-omnipotent, universe-creating god, the trick is to think big.

The WMAP mission measured the temperature of the cosmic microwave background radiation across the entire sky. This temperature was, in turn, directly determined by the location and density of all the matter in the universe during its very early stages (approximately 370,000 years after the big bang).

Now suppose that the WMAP data contained an artist's signature.

Any being that signed the early universe would have changed the nature of huge parts of the modern universe as a necessary side-effect of putting the signature in place. And if they signed it later, they would have needed to modify a volume of space billions of light-years in diameter. Either way, that being is more powerful than anything humanity could ever hope to even approach. It would definitely be worthy of the label "god". (We haven't actually proven that it created the universe, but if it claims to have done so, I'm not going to argue.)