I would not worry overmuch as to the tattoo.
First of all, for all I know it may mean "Department of Natural Resources."
In the strange ways of fashion, it may even be like a leather jacket was in the 50's: a way of saying 'look how cool I am.'
And, even if the meaning and intent is clear, and had been well voiced beforehand by the individual, there are still degrees of care.
A man who has just received a jolt, and has had complete cardiac / respiratory shutdown, may need nothing more than a good solid whack to get everything started again ... and be perfectly well 15 minutes later (See thread "Today I witnessed an Electrocution).
Another person may need hours of assistance before the drugs in their system let go; if they've been out a while, they just might never recover. Think "Anna Nicole Smith."
I believe such a "DNR" wish expresses the desire to not live on as an empty shell, in that limbo between life and death. (Terri Schiavo, for example). I believe they are saying "no heroics."
I do not see any such desire having any effect in the event of an accident. Once the body is at the hospital, and the long-term issues become relevant. Do your best, and let the lawyers argue later.
