Evidence need not be visual. We actually discussed this way back when in the evolution topic. The planet Neptune was discovered using math - in other words - its apparent effect on other bodies. The Earth has NEVER been directly observed orbiting the Sun, however we have a wealth of evidence that says that it does.
I suppose that I cannot definitively state that vampires, aliens and God do not exist, but there is simply no evidence that they do.
Again, the bible seems to play in to the fact that the writers knew that they would have to sort of protect themselves from the assault of logic. Such things as God saying that "no man may see me" and that other passage that I wrote above, to me have a singular purpose that seems to conveniently work with my view of things.