A frequent question - but what is interesting is that typical modern man cannot be convinced by revelatory miracles, because he does not believe them possible.
Reported events which would have been regarded as convincing by people of the past are now always and inevitably written-off as having some other cause - such as an illness (eg an hallucination or delusion), or self-deception (wishful thinking) or as being a manipulative lie.
For example, yesterday I was thinking hard about some metaphysical theories, jotting the conclusion down, then closing my eyes to think more; when I briefly nodded-off and had a dream in which somebody whom I knew and loved who had died, appeared and told me that my theorising was correct, and that they were made happy by it.
I jotted this dream down after awakening, and at first regarded it as a divine affirmation. But by the next day, being a modern kind of person, I had come to regard the dream as doubtful or wishful or just random - and it had lost most of its affirmative force. The dream made no difference either way - it was an epiphenomenon...
Yet mine was, on the face of it, pretty much the kind of dream we know from the Bible, upon which the fate of Empires might hang (the Pharaoh's dreams) or the fate of Christianity (Joseph, husband of Mary's dreams). From this perspective I might be making a very large error in dismissing my dream on the pre-decided-cultural-assumption that dreams 'cannot be' of any relevance to truth.
Nowadays, even if many, apparently normal, people are witnesses; then miracles (like Fatima - look it up) are effortlessly written-off (some kind of mass delusion/ fraud, perhaps?) - because modern people know they just cannot be true.
But this applies even when miracles happen to ourselves. In the extreme of experiencing something impossible while in a clear state of consciousness, many modern people will assume that they must have had a psychotic episode of some sort, rather than regard it as a divine sign.
Taken in this larger, historical perspective; many or most modern people are bombarded with divine signs and mini-miracles and revelations on a frequent basis - I mean things like significant or predictive dreams, precognitive convictions, visions occurring in states of altered consciousness, synchronicities, powerful feelings of knowledge, telepathy, sudden unexpected abilities or achievements or serendipities, or healings...
It is not that we are - most of us - short of experiences that would have been regarded as evidence of divine intervention; it is that we have already decided that such experiences cannot happen, and we are fore-armed with a spectrum of alternative explanations.
What is needed is not some overwhelming experience that would prove, once and for all, that God is real and exists - because these have already happened many, many times - in general and to ourselves - and we always manage to ignore them.
What is needed is a change in ourselves - so that we at least regard such things as genuine possibilities; and also that the truth is never found by having only one possible explanation for an event. Everything that happens requires interpretation - whether in science or in real life.
(In science and life; theory comes first, because it is the theory that determines what counts as evidence.)
So it is, in principle, impossible for anything to happen that could only happen as a consequence of divine intervention - there will always be other possibilities.
Having acknowledge the possibility; it is up to each of us, as individuals, to evaluate and judge whether any particular event was a divine sign for us - or not. And if we do decide it was a divine sign, then nobody else should be allowed to gainsay the fact!
Doubt is an over-abundant hence cheap commodity nowadays - conviction. meaning and purpose are the rare and precious treasure of our age. When God gives us these, we would be ungrateful and self-destructive idiots to reject them.