There are various elements to a DNR, including orders not to intubate, not to do chest compressions, not to employ vasopressors (medication to artificially elevate blood pressure), not to give food and/or fluids, not to use dialysis, or to use comfort measures only. The exact nature of the DNR order, including any and all therapies that may or may not be used, is explicitly elucidated in a signed document that is supposed to be readily available for medical practitioners to see. That way there can be no ambiguity if an unconscious yet terminal patient is brought to the hospital. The papers are supposed to be easy to find, though sometimes they can be difficult to track down.
Sometimes, however, the DNR is, well, let's just say sometimes it is slightly more prominent: