The thing is, atheists don't have symbols. Not one. The Darwin fish isn't a symbol of atheism. Jesus, god, and the bible are all symbols of Christianity.
You're still confusing "lack of belief" with "belief of a negative", a logical fallacy. Another logical fallacy is proving something doesn't exist. We call that argumentum ad ignorantiam. Believers make the extraordinary claim that god exists, so the burden of proof will always be on those that believe.