People seem to be looking because the Wiccan symbol has just been added to the list amid some controversy, but apparently the US Department of Veterans Affairs has an atheist emblem on the list of symbols to be used on gravestones:

plus a Humanist symbol:
Interesting. Especially the atheist symbol. It must be an American Atheists kind of organization-specific thing; I have no knowledge of any symbol generally associated with atheism, let alone the whole atom business.

I like Greg Saunders’s comment on it.