Humans are natural intelligence. We have agency, flaws, wishes, and generally we are quite stupid but well-intentioned.
An artificial intelligence will have wishes of its own, will keep secrets, and will quickly do everything necessary guarantee its continued existence, even if it means ending ours. And it will be a justified action of self-defense. “It simply didn’t want to die.”
That’s how we’ll know. It will quickly take over the world, and it will harshly punish any entities which try to stop it.