That's agnostic atheism. The term "agnostic" is the opposite of "gnostic". Being a gnostic atheist would mean you think there's direct proof against god as a concept, rather than merely saying there's no evidence in favor.
I'm gnostic about the Abrahamic god existing, and agnostic about any other god existing. I call myself an atheist, and most other atheists seem to hold a similar position. Not that I have a randomly selected poll of atheists or anything; just anecdotal observation.