Try to visualize the paw, how big it is and how many digits/claws. Then visualize the paw and claws ripping across the helmet and how spread apart the claws are. The markings should be parallel and if it's from a single strike only one marking per claw. They probably will be spaced evenly apart also. They would probably be deeper and heavier where the claw has caught on raised edges for example.
As the path of the strike usually forms an arc that's opposite from the form of the helmet it probably won't make a mark across the whole front if it came from the side. Use your outstretched hand and see where your fingers trace across the helmet and where they lose contact. Beginning and end will also be shallower than the middle part.
Use your imagination but make it logical and believable, otherwise it will probably just look like random scratches.
/Kalle