Appearance
Appearance reflects how your character is perceived by others and depends on all worn attire and held items. Wearing any piece of military clothing will cause your character to be identified as a combatant. This means enemies will shoot on sight and mark you as wanted - the same applies to openly carrying any type of weapon.
Bloodiness
Wearing bloodied apparel will also make you a combatant, even if it’s civilian clothing. If you get wounded and start to bleed, your clothing will become soaked and leave you suspicious.
You can clean your clothes by swimming. You need to fully submerge yourself in any kind of body of water - be it an ocean, lake, or river.
Note that blood is not visually shown on your character preview in the inventory screen. Instead, you will see a tooltip located next to the money balance.
Vehicles
Driving military vehicles as a civilian will make you combatant, even if the vehicles are not armed.
Settings
Depending on your difficulty settings, you may see a status icon denoting whether your character is perceived as a combatant.
By default, the absence of a shirt, pants, or boots will cause your character to attract enemy attention. After all, someone running around in only their underwear is bound to look suspicious.
Bloodiness effect on appearance and its intensity can be also turned off in settings.