I speak as a theist, but pigeonholing is the problem with labels. I think all kinds of things to be true that cannot be proven; so do you. It seems to me that it is reasonable to allow that a person may hold the existence of God cannot be entirely disproven by evidence, but that he simply does not think there is a God. If one personally does not believe there is a God and identifies as an atheist, they are an atheist, whether or not they regard that such a view can be proven. Similarly, if one thinks God may or may not exist and are unsure either way, they are agnostic.