So, then I take it you don’t KNOW or have direct knowledge that there “is no Supreme Being”.
Ok, then you’re an Agnostic....
By your logic every human on Earth is agnostic because it's impossible for any experiment to prove or disprove whether God or any other religious or supernatural being(s) exist. People just have to decide what they want to believe, whether it's a specific religion, a lack thereof, or a "spiritual but not religious" kind of thing.
Personally, I just accept people's labels for themselves. If a person says he's Christian, atheist, agnostic, Jewish, whatever, I'm take him at his word and don't try to say "well, uh, actually I say you're not!!!1"
Thankfully, it doesn't really matter what beliefs (or lack thereof) a person has as long as they treat others well.