Permanent Residence
Aliens in the United States staying for more than thirty days are generally required to register with the Federal government pursuant to the Smith Act and carry proof of registration at all times; for permanent residents, the proof of registration comes in the form of a Permanent Residence Card ("Green card") while, for other aliens, this can be in the form of either an Employment Authorization Document (EAD) or the I-94 card together with a valid passport.