I like to read articles about atheism written from a Christian perspective (it hones my understanding of where Christians are coming from), but I'm having a little trouble getting past the chronic misspelling of atheist as athiest.*
It's a-theist, as in not-theist,
not athiest, the superlative of athy: athy, athier, athiest.
Using my vocabulary skills, I can deduce from this context that athy must mean something along the lines of hopeful or optimistic:
But the athiest group hopes the ads will bring together residents who follow a humanist way of thinking.
*I wish to reiterate my mocking policy: Misspellings, minor grammatical errors, and punctuation faux pas are to be forgiven when they appear on a blog, in a personal email, or in handwritten correspondence. For my part, I am notoriously overgenerous with commas and am a poor typist. I reserve the right to mock these same errors when they appear in headlines, on printed signs, or in any other text that has been through an editorial process.