As most have said: evidence. However, just because god proved to me he/she/it existed, doesn't mean I would want any part in following/worshipping him/her/it. There's a lot of evil in this world that god would have to explain before I even considered supporting such a being.

Same things that makes me believe in France or Radio-waves or anything.
Credible proof - ideally him (her?) making their holy text appear in the hand of anyone who asks, written in their own language. Wouldn't that solve every question about the right god and the right version of that god's holy book? (Question for believers - why not do that?)

Maybe a stroke or brain cancer. My late wife had a brain tumor but her atheism had been ingrained since childhood and she sent a message of "no tears and no prayers.
This is the real world and there is no magic or supernaturalism!

Nothing! There is on endemic evidence in the existence of a god or gods. They are a construct of the human mind, looking for explanations for the world around them, mostly in a pre-scientific era. Unfortunately, religious organizations have become so rich and powerful that they keep brainwashing people, especially children, into believing that there is a god, and that science, (which is provable), is the lie.

Suspension of independent thought

Complete physical, irrefutable proof.

Nothing. Maybe aliens if they should show up, but not gods.

An extremely skilled Hypnotist expert & an overdose of a drug that makes one believe anything.

Evidence.

For starters, (s)he (them or it) should deposit a very large amount in a Swiss bank account set up in my name. Once it's there and I can withdraw funds (as long as it's not a bank holiday), then PERHAPS I'd believe. And I don't want to co-sign for the funds.

Either show me something clearly supernatural or give me drugs to turn of my sense of reason.

pardon, are you pertaining to the God of Moses, the God Almighty? Many people specially non-Christians believe in the gods of earth elements like fire and water, farmers in the god of harvest, etc.

And even Christians of the Catholic denomination believe in so many gods. But that's not surprising because, according to historical accounts, the Emperor Constantine's condition for Rome to become Christian, thereby averting the escalation of civil war, is to adopt Pagan rituals and traditions.

And there is also a mention in the Bible about a "council of gods".

I don't know if those whom we call "aliens" (in their UFOs) have a god of their own but I'm sure they have a leader. The scientific and high technology communities keep mentioning about advanced alien technology

nothing would make me believe in a god, as we understand the term. nothing. if a god came down from, let's say, a heaven, and announced himself, i would call my shrink.

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Nothing!!!

The only thing that might make believe is if shit load of people just up and vanish like 100's of millions or more. then i might re think stuff about god.

If this existential being showed it's non existent face.

Well, a conversation would certainly help. But it's got to be at least a half hour...

I'm not sure but one way would be, after I die, I heard a voice say 'Well you got one bit wrong didn't you?', but then to prove he really is the man he would then say 'No matter, the kettles on, make yourself at home'. That might do it

They could show up in public and hand out cotton candy for free, and maybe do a workshop on divinity

He would have to raise to life several of my dead friends that died in tragic circumstances (suicide, murder, cancer). I would then have to consider my fallibility.

I would need, at the very least, the slightest credible, verifiable evidence of some sort of deity.
basically, I am unconvinced of extraordinary contentions by mere anecdotes and fallacies, as are most people normally, unless it's a conveniently unfalsifiable, emotionally satisfying myth that they were indoctrinated with before being old enough to think critically.

While I tend to err to the scientific, materialist side of things like most people on here, I'll be generous and give God an easy way out: Pull a fully grown dancing gorilla directly out of Trump's a-hole on live television, and I'll be in the first row pew at the early service on Sunday. My offer has no expiration date.

Do you mean as a specific entity? An anthropomorphic being? My mind just cannot comprehend such a thing - I rejected that when I became atheist. So, if such a being came to earth, I would be doubting my sanity and heading for some help.

Just think of all the ways that God, if real, could immediately and irrefutably prove its own existence. All sorts of miracles might happen. Manifestations. Immediate simultaneous subtle shifts in the neurochemistry of seven billion people to cause them to all believe in the same way.

The Apocalypse -- not some stretched interpretation of current events, I'm talking a literal horseman galloping all over the earth, leaving plague or famine in his wake, or a beast with the number 666 tattooed on its forehead emerging from the bowels of the earth being accepted by all of the nations of the world as their king.

If you want a sample miracle that would convince me, I'll offer: "amputated limb regrows after prayer for same."

Yet despite all of this, and despite the fact that for an omnipotent, omniscient deity doing any of these things would be by definition easy, none of this has ever happened and we all know that none of it ever will.

Verifiable proof.