I know about DNR in the U.S. I also know that individuals also utilize a living will and advance medical directives in which they make their wishes known. As far as weaaring some type of necklace or tatoo, don't know if that would be reliable or not to indicate someone's choice.
I have been given several directives personally, but I always have urged family members to put it in writing so it won't just be my word against others' wishes. Of course, they never get around to it.
Thanks for sharing.