Well, in the mind of a doubter. A dragon could leave evidence of his presence, but the evidence still may not be evidence enough that it was a dragon. For example, a dragon can breath fire into the dumbster, but for all we know it was a human that set the trash on fire. This reminds of me of big foot. People are claiming evidence all the time. But doubters always have an explaination for those evidence.
I don't think this world is evidence enough of God's existance for an atheist. Now, I can not say I know the mind of an atheist, but I am trying to understand them. For example, in their minds, the earth could have always been here just in different form, which I read from a poster on here. I've also read some of them think that it was an accident. I read what other scientist believed. But everything is just theories. They have explainations for everything that's not God. Proof could stare someone in the face, but it may not be enough proof for the doubter, unless they see God face to face. Scientist can come up with many different explainations about this or that as we well know.
Now, when Jesus stood before his accusers they said to him "if you are the Son of God, turn these stones into bread." Jesus just stood there. He was also asked "are you the Son of God?" Jesus said "it is as you say. And you will see the Son of Man sitting on the right hand throne of God." That's the burden of proof. It's in the future. This is what it's going to be like when God reveals himself to the world. We can't use human scientific reasoning to prove the existence of God. Jesus did not. Now neither can we.