Depends where you are. Yes, when someone has our state-issued DNR/Comfort One bracelet there is a piece of paperwork with that, but for our purposes the bracelet is good enough. It has a window through which EMS can see the patient's name, DOB, and their doctor's signature.
If the bracelet is all they have (unaltered or damaged, a closed bracelet attached to a necklace worn by the patient is also allowable), it's valid for us. They do not get worked (or bagged, or monitored, or receive an IV for resuscitation drugs). If the state Comfort One form is present, well, ok. I don't need it though.