Originally Posted by After Shock Media

Yup in the US they can do a couple of things. One being getting an injunction so that they can prove that you are of not sound enough mind to make such a choice. If you have a living will or a few other such contracts, they can also strong arm the legal decision maker into what they way. Then of course if they get a body in with some life, no family etc. They can do whatever the wish to stabilize the person until identity and family is reached. A note alone would not prevent them from doing it, unless they were on your side of the fence.