First of all, I'm not aware of any unique "Atheist Symbol". The one that you refer to belongs to American Atheists. Others include the Scarlet letter A, Empty Set symbol, Darwin Fish, FSM etc. However, while individuals and organizations alike may pick any of them (or come up with new ones), given the absence of any central doctrine, none of them can be regarded as "The Atheism Symbol".
Secondly, the symbol you mentioned, one that originated from a specific organization, is not supposed to represent atheists in general, it represents what they consider atheists should stand for. And what they hope atheists should be like is smart, scientifically-minded, educated free-thinkers and the symbol captures that quite well.
Secondly, the symbol you mentioned, one that originated from a specific organization, is not supposed to represent atheists in general, it represents what they consider atheists should stand for. And what they hope atheists should be like is smart, scientifically-minded, educated free-thinkers and the symbol captures that quite well.