A poem on the underground wall

The last train is nearly due,
The underground is closing soon,
And in the dark deserted station,
Restless in anticipation,
A man waits in the shadows.

His restless eyes leap and snatch,
At all that they can touch or catch,
And hidden deep within his pocket,
Safe within its silent socket,
He holds a coloured crayon.

Now from the tunnel's stony womb,
The carriage rides to meet the groom,
And opens wide the welcome doors,
But he hesitates, then withdraws
Deeper in the shadows.

And the train is gone suddenly.
On wheels clicking silently
Like a gently tapping litany,
And he holds his crayon rosary
Tighter in his hand.

Now from his pocket quick he flashes,
The crayon on the wall he slashes,
Deep upon the advertising,
A single-worded poem comprising
Four letters.

And his heart is laughing, screaming, pounding,
The poem across the tracks resounding,
Shadowed by the exit light
His legs take their ascending flight
To seek the breast of darkness and be suckled by the night.