Two things to try...1) make a paste of baking soda and warm water, and rub it on the marks with a soft cloth. 2) put some hairspray onto a Q-tip, and rub the marks gently. One or other of these tips should work. Let us know.
Nail varnish remover will remove biro from practically anything, including clothing (except silk and satin of course). It also removes Elastoplast marks left on skin.