Manumission papers would be provided by former owners to their newly freed slaves. By the middle of the 19th century in Georgia and other states freedmen had to register with the state, providing proof how they became free, whether by birth or manumission.
Follow up: how seriously was this proof, if there was any method, taken?
I've always held the impression that freed slaves really didn't hang out in the south because they risked being enslaved again, regardless of 'status'?
Further ... what were the consequences faced should the freed person be unable to provide their papers? If the papers were lost, or damaged, for example.