Several options depending on how deep they are. You can mix Cerium Oxide powder into a paste and rub them out by hand or try Jewellers Rouge.
If they are fairly deep you're going to need to be fairly aggressive. I've used Micro Mesh in the past to remove scratches where a previous owner had caught a ring or something on the glass and for all it's far better suited to plastics, it did work with a fair amount of elbow grease.