It was recommended to me by my cardio and my pcp that I consider a bracelet but I break watches and jewelry when I wear them, and I can't where them when I am working anyway. (It is asking for trouble to wear bracelets etc. while working with machinery.) My solution was a small tattoo on my left wrist with the medic alert symbol and "warfarin" on the inverse. I could have written anti-coagulated but warfarin looked better. I figure any EMT should be able to figure that out. I also carry a wallet card provided by the valve maker and that to may not be as good as having all the info on the medic alert system but it does have the hospital and pcp phone numbers and they have all my records.
Not for everyone but it was the best solution for me.
edit: The answer to the first question that most people will have of this post is that I will just add info if necessary, or change it. Tattoos are only MOSTLY permanent!