This is the symbol of the American Atheists.
Links: explanation of the symbol by said godless ones; remark on its existence by Justin.
Questions: Do atheist organizations in other countries have their own symbols? Is there a similar symbol for us agnostics? I don’t know. Do you?
Updates: I meant to mention that I am neither American nor atheist; my original misspelling (athiest) lives on in the post URI; I rather like the word athiest, which probably mean “most athy.”
One word: BLING!