Is nihilism the logical extreme of atheism?

[Angrboda]

Every atheist I know assumes that the brain adequately serves as the interpreter of signs. There is a problem with this assumption. Brains are themselves sensible objects performing material processes and like all other physical things have no meaning.

That every atheist you know holds a certain position doesn't make that position a logical extension of atheism.

Neural correlates are like abacus beads that require the interpretation of a knowing subject .... God or gods provide a basis for value that atheism lacks: value is contingent on [a] non-physical interpreter[s].

This is an interesting assertion, but again, reductive materialism is not a logical extension of atheism. I would agree that it's possible that value is contingent on a non-physical interpreter, but what is your argument that this is indeed the case? If you're arguing that reductive materialism hasn't explained the operation of meaning in the world, or that you can't imagine how it could, then that's nothing more than an argument from ignorance or incredulity. I will concede that reductive materialism may have failed in this area. That doesn't make your assertion true by default. I'm not an atheist, but my belief is that the common understanding of the nature of meaning is an illusion, an illusion consisting of material processes. This introduces a third option which you seem to have failed to consider, which renders your formulation a false dichotomy.