You could just add a charm to your Tiffany. Try this site:
http://www.americanmedical-id.com/ They have quite a few nice options, and you can order just the charm with no chain. They also offer a membership to www.myomr.com, which is an online medical registry. My dd's and i all have med id's (the traditional kind) and a small tag hangs off of them with the website address and a code that gives medical ppl access to all my medical history, which I put on the site myself. It is awesome! You can order just the tag itself with the online info, but then emergency medical personell would have to get onto a computer to access all your allergies, which may not help you out at all in an emergency!
I agree w/ the pp, if you have any life-threatening allergies, you should be more concerned with making sure the tag is found and not overlooked.
BTW, what is so special about a Tiffany bracelet? I have never even heard of them, so I don't know what is so great about them! I am not being rude, I am just curious!