I'[ve been looking for a medic alert type item for my Dad who is allergic to penicillin and spoted these doen from £10.99 to £5 either pre engraved with a number of conditions/allergies (ie asthma, penecillin allergy etc). They are a stainless steel tag approx 1.5cm wide by about 4 cm long on a 26" stainless steel chain. They were on the display at the pharmacy counter.
They feature the medic alert worldwide recognised symbol so will be useful all over the place should an emergency occur.
Hope this is useful.