But critics of the practice say paramedics and emergency room doctors might not notice the tattoos, possibly leading to incorrect treatment.
"On the surface it doesn't sound like a bad idea, but there's a few issues that we have with it," said Robert Ridge, president and CEO of the Canadian MedicAlert Foundation.
"The first is paramedics have been trained in Canada for over 50 years to look for a medical alerting ID, usually on the wrist or the neck," Ridge told The Canadian Press on Monday. "So MedicAlert members either wear a bracelet or a necklet or a watch. And emergency responders have been trained to look in those places for any medical alerting information."
And it's not only emergency responders who use the system, he said. "It could be anyone. It could be a member of the public who comes across someone in distress and is able, through the MedicAlert ID, to call the hotline and help the person."
Ridge said members of the charitable organization wear MedicAlert devices to identify themselves as having a range of conditions, from diabetes and epilepsy to life-threatening allergies to peanuts or certain drugs like penicillin.
Vancouver tattoo artist Andrew Warren said that during his 12 years in business, he's had a "handful of folks" who wanted a medical-related tat.
In fact, many of those clients were paramedics, he said Monday. "And that's the weird thing, because they know it can't be taken at face value."
Most of the inked designs appear to have been for esthetic reasons, not as a way to alert emergency responders, Warren said. "And a lot of times, travellers get it, backpackers and stuff, because in other countries they will take it at face value."
While many people have such tattoos on their arms, he's also put them on other body parts, including the back.
"I did one on a gentleman who had a heart condition, and I did it on his chest. It was something along the lines of ... letting them know he had a weak heart," Warren recalled.
"For the most part, there's not a lot of function to it," he said. "One of my old co-workers has a memorial to his pancreas because he's diabetic. So it was like a little pancreas with R.I.P. written underneath."
It's not known how many Canadians have opted to engrave a medical warning in their skin, but it appears to be a growing trend in North America.
Reasons vary: some people can't wear jewelry on the job because of the nature of their work, while others find bracelets or necklaces can break or get lost. Still others have allergies to metals like nickel that the jewelry may contain.
But Dr. Saleh Aldasouqi of Michigan State University, medical director of the Sparrow Diabetes Center, points out that unlike medical alert jewelry, there are no guidelines about tattoos' designs or where they should be located on the body.
"This thing has to be standardized," Aldasouqi, who has written on the issue in the journal American Family Physician, says in the CMAJ article. "We have to at least teach and educate emergency personnel so they become more aware."
Ridge worries that having a tattoo instead of a standard medical alerting bracelet, for instance, could give a person a false sense of security about what happens in an emergency — and how important it is for paramedics and doctors to have clear, concise information.
"All we're doing is speaking for you when you can't speak for yourself and we're saying what you would want to say in an emergency situation," Ridge said of medical alerting devices worn around the wrist or neck. "Quite often that information will help save your life or protect your life."
But a tattoo's legibility can fade over time, and it's difficult to update critical changes to a person's medical condition on a design already inked into the skin, he said. "Even if the emergency responder saw the information (on an existing tattoo), it could be misleading."
"In order for information to be useful, it has to be accurate (and) it has to be very quick to access."