Along the lines of what PIKKA said, I've seen on a TV show where they rolled/balled up a piece of white bread and rubbed that on a mark like an eraser. I've also seen them use regular eraser.
By
09/03/2009
Can you give an idea of original cause? Try lifting with scotch tape pressed down on the spot, then lift off, then try to 'clean' with wadded up ball of white bread, also pressed and lifted. If pencil, use eraser after these steps.