you could polish them, with a light steel wool pad, or if you have a buffing wheel or a buffing bit on a dremel. you'd have to start with a heavier roughness than polish the scratches back out of it---a lot of work IMO. but what do i know?
ultegra cranks though (all shimano) usually rub off because of the design, so go ride them off, thats the coolest way.
jb