Use the object filter to look for "MarksMale" or "MarksFemale", drag & drop these into the "Additional Head Parts" box/list in the Character Gen Parts tab of the NPC window.
The human scars are not properly rendered in the preview screen. As long as you export facegen data (Actors Tab/Highlight the Actor you want to export facegen data from/ Ctrl + F4), the scars will show ingame normally.
So the scars appear when preview the full body but not the head, weird.
That just means that they're attached to something outside of the 'head' area. Arent' scars on more than just your face? I always thought they were on your chest/back as well. If so that would be why, if not, then it's just quirky bodypart assignment.