We (atheists, freethinkers, rationalists and assorted brights) need a symbol under which we can unite, much like the Christian fish.
The fish had (and has) several virtues from the point of view of a group of people who needed to proclaim their beliefs to others who shared them, and oftentimes conceal those beliefs from those who would persecute them: it had significance for believers, it was instantly recognisable, it was obscure in meaning to outsiders (though it, and its meaning, rapidly gained recognition) and it was easy to reproduce in many different media, by people whose command of graphic design or written language couldn’t be taken for granted.
We rationalists need a similarly simple symbol to denote our adherence to beliefs based on provable facts, and our naturalistic, rationalist worldview. I’d like to propose such a symbol:
The magnifying glass. Simply a circle and a stick. It can be drawn roughly or precisely, it can be incorporated into other designs, or it can be rendered in three dimensions – as jewellery, for instance, or sculpture.
The magnifying glass (we could refer to it as the rationalist lens) represents rational enquiry, scientific investigation and curiosity about the natural world. Like the Christian fish, it’s easy to reproduce in two or three dimensions, formally or informally. It can be executed as calligraphy, typography or jewellery. It’s simple to remember and easy to explain. And, if you’re of a subversive turn of mind or otherwise need to conceal your affiliations, it makes (like the fish in its day) an excellent piece of clandestine graffiti.
But perhaps most importantly – unlike, say, the scarlet A proposed for atheism – it defines us in terms of what we are – rational – rather than what we’re not – credulous.