How do I clean these gloves so they do not leave marks?
Clean rubber gloves can still leave marks. My guess is that the finger pads are more wornout (at microscopic level) and you've reached the not so smooth 'meat' part of the rubber that will stick and rub off on things.

Try with new gloves, or surgical latex gloves, or if marks on glass drive you nuts (like some of us), you can try microfiber gloves over rubber gloves.