The idea of adopting an official (or semi-official) symbol for atheism is something of a hot topic. And when the idea gets floated on such a signpost blog as Pharyngula, it is immediately drowned in comments. To be fair and respectful, I read about it again on Heathenz blog, which I also read, despite my usual dislike of the use of 'z' where 's' would work just fine. I began to post a comment and then decided to expand my thoughts here.
I think that it is fun, and the conformist in me wants to adopt a symbol - personally I like #89 - but there is an element of danger when a group that constantly claims to be nothing more than literally nothing begins to adopt symbols to signify their allegiance to said nothing.
There isn't anything wrong with atheist communities and groups, and those groups and communities are perfectly welcome to adopt symbols of their own. I support this, in fact. Dawkins' 'Scarlet Letter' is a symbol of a particular campaign, a specific idea. A symbol for atheism in general, however, is a bad idea. A symbol must represent a specific idea, and, aside from 'There Is No God,' there are no specific ideas about atheism.
So picture this in five years or so. That symbol will have evolved and, like any good meme, will have picked up some baggage. Who knows what those extra ideas would be, but it doesn't really matter. Atheists may wish to belong to a group, and they can. You can join the Atheist Alliance or the Center for Inquiry. If neither of those groups suit your specific needs, find another or create your own. It is natural, I think, for humans to wish to belong to a community, to identify with a cause. This is why the idea of an atheist symbol just will not go away.
But it should go away. I am proud of my atheism (a little cautious here in North Carolina) and would love to run up a flag or get a tattoo or bumper sticker. And they exist, but each one carries more baggage than simply declaring that there is no god. As soon as there is such a symbol that claims to speak for all atheists, it is time to find a new word.