Medical staff are trained to look for a variety of things, not just simple jewelery.
As long as it has a caddeceus on it, in a place normal jewelery is found, then they'll see it, and inspect it.
Some of the ones sold by the medic alert company are pretty fancy.
Personally, i have a card in my wallet, and am getting a tattoo on the inside of my wrist.
A stylised caddeceus, with my blood type and Type 1 diabetes written around it.
Anything that suits you, that you will not forget. Doesn't matter how practical it is, if you don't WANT to wear it, then chance are sometimes you won't. Which makes it rather pointless lol.