Is atheism a belief?

[downbeatplumb]

Would you feel better if I said that you, like many other agnostic non-theists, find reason to clarify for others that you're not expressing a positive belief?

Nope.  "Agnostic" is a better descriptor for me, tyvm.  Check it out:

Q: Do you believe in a God / gods?
Me: I don't know.

I can, upon further questioning, explain why I feel the term agnostic suits me better, and have.  I can also provide dictionary or wikipedia posts showing that my use of the word "agnostic" is among accepted definitions, but I'd assume you know that already.

Of interest, perhaps, as that "agnostic" itself can be viewed in a couple of ways.  It can be (agnosis + ic = adjectival form of not knowing) or (a + gnostic) as in "not among those who claim a gnostic tradition."  This is interesting because it is something that the wooiest Christians and the most materially-minded have in common: they have some sense of knowledge, and in a way that I consider faithful.  A Christian will point to Genesis.  A material monist will point to the Big Bang, and will never say "We don't know, and can't," but something more qualified and hopeful, like "We don't know. . . yet!" or "We don't know. . . but if we ARE going to know, science is the best vehicle for arriving at that knowledge."  I shy away from this kind of talk, because it's not at all clear that the latter is the case.

If you don't know if you believe then the answer is that you do not believe and are in fact an agnostic atheist.

It is binary, it could change from second to second but at any given time you are either and atheist or a theist.