These medals represent two progressive ranks in marksmanship qualifications. The first rank is Marksman, the second rank is Sharpshooter. (A third rank, Expert, was possible).
Many military analysts give a significant share of the credit for the astounding performance of the Marines in WW1 to their outstanding marksmanship. Attaining Sharpshooter qualification was considered a significant accomplishment by Dad's contemporaries.
Reference pictures of these medals show that they had a blackened background, with only the raised portions showing silver.