I believe in God. I didn't always and used to be an agnostic/sort of determinist. I understand those with doubts, trust me I do. For those that do not believe at all, I propose to you an experiment - of sorts. Make a request either in your head or vocal, it doesn't matter. Call it a prayer, or not, again it doesn't matter. You need to be sincere in this request, but you don't have to prostrate yourself or utter biblical passages. Ask something along the lines of "If there is a God, would you reveal yourself to me?". You can even explain the extent of your disbelief and the constraints of logic that prevent you from even considering such a thing...except in this request and in that there may be things hidden from your senses. The scientist in you can even consider this an experiment. You can even approach it with reasonings that there may be some sort of primal psychological trigger in the subconscious that reacts to this sort of request and models an interpretation of some event to fit a pattern qualifying as a response to this request.
I can't tell you what results you will get, but I can tell you that something will occur that will make you think back upon your request with some wonder. It may not be today or tomorrow, but it will happen. Those firm in their disbelief will immediately wish to qualify the event as pure coincidence, but they will find something within themselves gnawing at that reasoning. You might well end up still holding to your original position, but you will find the certainty of your convictions somewhat lessened and instead of knowing there is not God, or having doubts in the existence of God you might well find yourself with some doubts to the non existence of God. I don't consider this an unreasonable thing for me to ask you to do, and again along the lines of scientific study I wouldn't consider performing the request to be unreasonable either.