I was at the rehab hospital, after my accident, last year. I have a bicycle tattoo on the back of my calf. My physical therapist said that considering the fact that I was there due to being struck by a car while on my bike, it was her second favorite tattoo seen on a patient.
So, of course, I asked about her favorite tattoo. She had a patient several years ago with "DNR" in bold, capital letters on his chest.

I suppose that removes all doubt for EMTs.