Thanks for the tag
@DCUKMod 
First Responders, paramedics, EMTs etc won’t initially hunt for medic alert jewellery if they find an unconscious patient, they’ll be too busy establishing that it’s not a breathing, bleeding or cardiac arrest issue. They’re the priorities. Once all that has been dealt with, they’d start investigating other causes for your unresponsiveness, including a BG test.
Having said that, it doesn’t hurt to leave a trail of clues, as training includes an assessment of the scene on arrival, and constant collecting of information. My dog tags around my neck would be quickly seen if they needed to be removed for a zap with a defib, for example. A bracelet stands a 50% chance of being spotted when they take your pulse (assuming you have a heartbeat, if not, you’ve got bigger issues than diabetes
). Tattoos aren’t taken as gospel, because people have medical looking ones for all sorts of reasons, often as a tribute to a loved one with that condition. Emergency medics wouldn’t check your phone for medical information, although the police probably would if they were involved.
I wear dog tags with mine and my next of kin details on one, and a caudacus medical symbol and insulin regime on the other. I have a tiny, tubeless insulin pump that can be anywhere on my body and could be easily missed - it could be on my calf, or back, for example. So I have made a point of having “Omnipod insulin pump NOVORAPID” on my tags, as well as on a red pet disc on a beaded bracelet, on my car key ring and on a bright red star keyring on my handbag. It’s a trail of breadcrumbs that should hopefully lead someone to realise I use insulin. I don’t wear all of them all of the time, although if I’m alone I usually do.
I wouldn’t get a tattoo, not just for the reason above, but because all my ink celebrates things I love, and I don’t love diabetes.
