At the risk of traumatising the character art team, I could think of a few ways that a cutthroat galaxy might mark its inhabitants:
- Plasma scarring: spiral spatter marks
- Flechette wounds, puckering. From heavy handed police units
- Radiation burn marks
- Plain old burns
- Parasitic Infestation marks
- Heavy metal poisoning discolouration
- Genetic level branding on escaped slaves
- Vacuum exposure scarring, bloodshot eyes