Let's start at the very beginning...

Could there really be an alternative image for the debut posting on The Filthy Pen? Of course not. It had to be the male genitalia.

Marking territory in a manner unmatched by any other crudely-sketched drawing, the graffiti penis has been around since before records began. When prehistoric man picked up a bit of charcoal from the warm ashes of his very first fire, he looked at it, sniffed it, tried eating it, and threw it away. Then he noticed a powdery mark where it had hit the cave wall. Looking from the wall to the charcoal and then back to the wall, he felt his first creative urge swelling up. He reached for the charcoal, and guess what he drew with it? You've guessed it - a cock. And that’s how art was invented.

Fast-forward countless thousands of years, and look what we find - knobs to the left of us, knobs to the right of us. We're drowning in a sea of cocks. This misshapen specimen has been spray-painted on the wall of an underpass in the shadow of the Big W store on Milton Link on the eastern edge of Edinburgh. You can get a rough idea of its dimensions by judging it against the size of the bricks. Isn't it a whopper?

Although The Filthy Pen is happy to expose childish graffiti in all its guises, from the perfectly-executed obscenity through to semi- literate scrawls, penises are likely to be a recurring theme. There’s no Freudian sub-text, they’re just unavoidable really. Cocks loom large in the average graffiti artiste’s repertoire. They'll be coming thick and fast, so to speak.

It's a history thing, it’s a maths thing. Do the sums:

(writing tool x blank space) + idiot = graffiti cock

Q.E.D.