I (Niels) created the V for Voluntary symbol in 2007 in search for a new symbol that would capture the essence of the anarcho-capitalist movement and also carry a more positive message than other existing symbols.
The name is a play on the phrase 'V for Vendetta'. But where Vendetta involves vengeance and violence, Voluntary stresses peace, understanding, and looking forwards.
The colors of the symbol are yellow (or gold) and black. Yellow is a reference to gold, which was the market chosen money. So it's a reference to free market money, and by extension the free market and capitalism. Black is a reference to anarchy. Anarchy, or an-archy, means no rulers.
The shape at the top of the symbol represents a handshake, which is the most typical expression of a voluntary agreement. These two images illustrate how:
Vector and raster versions at wikipedia: for light backgrounds, for dark backgrounds.