Anybody looking to purchase medical alert/warning jewellery should register with MedicAlert. From personal experience, I can attest to the high quality and effectiveness of the service they provide.

http://www.medicalert.org.uk

MedicAlert provides your emergency medical details to those who need it, via their emergency telephone number (staffed 24 hours a day, 7 days a week). They are able to converse in over 100 languages. Sponsorship or your membership is available if you are unable to afford the small annual membership fee (which is around £30 GBP a year).

MedicAlert operates in other locations around the world, including but not limited to the USA, Canada, Australia and New Zealand. See http://www.medicalert.org/about/worldwide-locations.

The symbol on my tattoo is the (blue) Star of Life. The photo below was taken before the MedicAlert telephone number and my membership number were added, wrapping the star, top and bottom respectively.

The tattoo was done at Frith Street Tattoos in London. http://frithstreettattoo.co.uk

MedicAlert just use the Rod of Asclepius on their jewellery though.

I'd recommend anyone buying the jewellery to make sure they get an item where the emblem is in red or blue to draw the attention of the emergency services. Even better if you get the blue Star of Life instead of just the Rod of Asclepius. (From experience, a vividly coloured Star of Life gets noticed mucher quicker).

http://www.medicaltags.co.uk and http://www.universalmedicalid.co.uk are reasonable alternatives for medical jewellery (as long as you have a valid MedicAlert membership number to engrave on to them).