Im an OC EMT working for Pacific Ambulance was taking a patient to a doctor's appointment at White Memorial. On my way out I was stopped by an LEO wearing casual clothing and a badge. He asked to see my parking ticket and then asked me what time I came to pick up the patient. I told him that I brought my patient here from Orange County and am now transferring on the return. He then left me alone. He told me that he stopped me because he didn't see a DOT sticker on our rig.