xjwsrock - Any communication would need to be direct and to multiple eyewitnesses at the same time to eliminate the possibility of hallucination, schizophrenia, etc.
Actually... there are documented cases of people sharing the same or similar delusions. You can read this Wikipedia article about it. It is possible for multiple individuals to have the same hallucination or delusion—unfortunately.
Still, a normal (read: real) God would consider what you have just said. For instance, why would He allegedly inspire the Bible if He did not preserve the original manuscripts? (I realise this example is not exactly what you are talking about, but it still touches on unreasonable communication of a divine with humans.)