I'd prefer he come in human manifestation but do at least one miracle to prove he's who he says.
Was that not done already?
You won't be able to tell God from Adam (I remember there was a film like that).
Some believe. Some don't.
(John 10:31-33) 31 Once again the Jews picked up stones to stone him.
32 Jesus replied to them: “I displayed to you many fine works from the Father. For which of those works are you stoning me?”
33 The Jews answered him: “We are stoning you, not for a fine work, but for blasphemy; for you, although being a man, make yourself a god.”
(Luke 19:37-40)
37 As soon as he got near the road down the Mount of Olives, the whole multitude of the disciples began to rejoice and to praise God with a loud voice because of all the powerful works they had seen,
38 saying: “Blessed is the one coming as the King in Jehovah’s name! Peace in heaven, and glory in the heights above!”
39 However, some of the Pharisees from the crowd said to him: “Teacher, rebuke your disciples.”
40 But in reply he said: “I tell you, if these remained silent, the stones would cry out.”
Jesus did more than one miracle, and many did not believe him.
Why do you think you would?