I actually think a universal symbol for athiesm is a grand idea. Symbols in many instances may bind people together or represent the polar opposite of what the freedom of athiesm is supposed to represent, but I've thought many times how proud I'd feel to sport a sign of some sort showing I am a strong athiest and that I'm confident in my belief (of lack thereof), almost as a way to spite the groups that discourage us, but more so to show that when it boils down to it, we are a community, we are a group of people sharing the same interest, and we should show that we're glad to fight the pressure of the majority. Think about it, some fifty years ago homosexuals were just a disgusting (in the majority opinion, I for one support freedom of sexuality) random assortment of individuals, but then there were gay pride parades, parties, a universal symbol for gays, and publicity that showed the people they were here to prove themselves, to show they are going to earn their right to live equal, and you've seen how more accept they are today. A symbol would show we're not just a half-assed group of people that are lost causes, that this is who we are, that we are a kind of people, that we're athiest! It's a radical idea, but we should show our pride!
"Little one, I would like to see anyone -- prophet, king or God -- persuade a thousand cats to do anything at the same time." A Dream of a Thousand Cats, Neil Gaiman
Atheist aren't unified by any thing but an agreed non-belief and independence of thought. Beyond the non-belief, what they actually value is not unified and is based entirely on their personal opinion.
Symbols general stand to indicate a set of agreed values. It's hard to agree to share a symbol with someone you may not have your values.
You could set up a symbol for atheists who agree to follow a set Code / foundation of morals / life plan / world view etc. That would work. The symbol would not be for atheism, but as symbol for atheists with these values.
The red cursive "A" seems to be a more recent innovation. The one atheist symbol I remember from decades back is the atom with "A" for the nucleus of the orbiting (unseen) electrons. American Atheists initiated or adopted this symbol, I think. I can't think of another that has as much recognizable status. I think it would be a big mistake to use a symbol that could be confused with anarchism. I too have my doubts about an official symbol. But the symbol I like the most is the symbol for "humanism". It could be adopted by people preferring to call themselves atheists as well, if so many of them weren't such assholes.