Symbols of Disbelief (Atheism/Freethought Symbols)

Atheism throughout history has, understandably, been a pretty private affair. In recent years, however, the rise of the atheist/agnostic “freethought” movement has brought active disbelief into the public arena, creating not just a camaraderie of unbelievers, but a sometimes actively anti-religious movement. 

A number of atheist, pro-science, and related emblems have been proffered as symbols for nonbelievers, but none have any real consensus so far. I’ve compiled a brief, by no means exclusive list of some of the more popular emblems below.

Early symbols
One of the earliest symbols is not a symbol of disbelief per se. The Humanist movement’s “happy human,” designed by Denis Barrington in 1965 for the International Humanist and Ethical Union. The little figure symbolized the humanist philosophy of people over religious dogma, and while popular with atheists, is not an explicitly atheist symbol.

The earliest explicitly atheist symbol I’m aware of is the open-atom logo of the American Atheists, designed in the early sixties to place an emphasis on scientific curiosity and empirical thinking. While adopted early, it is not popular overall as it is trademarked by the organization.
The “evolve fish,” aka, the “Darwin fish,” a satirical jab at the ubiquitous “Jesus fish,” is one of several popular recent symbols:

The “invisible pink unicorn” symbol was intentionally designed as an atheist identification symbol. The image alludes to a common argument against belief, contained within the mathematical symbol for an ‘empty set.’  The first mention of the IPU appeared in the mid-nineties on Usenet, from author Steve Eley:

“Invisible Pink Unicorns are beings of great spiritual power. We know this because they are capable of being invisible and pink at the same time. Like all religions, the faith of the Invisible Pink Unicorn is based upon both logic and faith. We have faith that they are pink; we logically know that they are invisible because we can’t see them.”

So far, the real contender has been the “flying spaghetti monster,” which began as a variation of the “IPU” argument, but proved irresistable once reports of “miraculous appearances” of the parody deity began to roll in. FSM merchandise is abundant, and includes car medallions, t-shirts, posters, and more.
Other noteworthy images include the atheist ” Scarlet A” symbol, designed by Richard Dawkins for the “OUT” campaign, which encourages Atheists to be more outspoken:

The circle/A emblem, somewhat resembling the Anarchist “A” symbol:

The empty set (circle/slash) with or without cross (aka the “Bad Religion” logo), ghost, or other object representing religion:

I any case, the issue is far from settled, at least as far as consensus goes.