This is not a ubiquitous idea, but it could be. It’s also one of the better uses of QR codes that I have seen. Ideally if I had one major medical condition (e.g. a specific allergy), then I would like to see it written next to the QR code. Of course the advantage of the QR code is the ability to contain alot of information on a very small place, which is ideal for people who do have a number of medical conditions. Plus the stickers are cheap and you can have them everywhere.
For more information on this, go here: Lifesquare. Found via this article: Personal QR codes could help first responders get vital patient information | IBM Smarter Trends