A bondmark marks whether you are either a slave or free. If you have no bondmark, you can get a mark that sets you free, or you might get caught by a slave trader and be enslaved by them.
Either way, it is revealed that it is entirely possible to remove the bondmark.
Cole has no mark as he steps foot into The Outskirts, though when he is caught, he is given a bondmark marking a slave. Fortunately Declan removes his bondmark as well as his friends' bondmarks. They are then given a freeborn mark instead.