I recently found out that the EMT guys in the ambulances cannot honor a living will in Kentucky. They have their own special form that must be signed and notarized...otherwise they are required by law to try to keep you alive enroute to the hospital. I learned this from working with Hospice.
The easiest way to handle this sort of thing is a tatoo, across the chest.
If one wanted to be really correct, the entire Health Care Advance Directive could be tatooed, but that'd be uncomfortable to say the least.