Don't know about that, I was issued my first set by the Army, wore them for three years, and left them hanging in a wall locker at Fort Dix when I out processed.
I did three years USAR, got out, and was issued my next set by the USCGR before going to Saudi in 1990.
I was on the Bear in 99 over in the Adriatic, and never heard one thing about getting tags. However we didn't know we were going until 24 hours before we deployed, so maybe that's why
I was in from 1986 until 1996. I spent eight of my ten years in operational units. We were never issued them in boot camp and I never received any during my tour of duty.
I never had them when I served in the USCG from '82 to '88 but I think they are a good idea. Kind of nice to know the blood type right off should you get injured. I don't know how simple it is for a hospital to determine...maybe all of a minute but still.
My son has them with the Marine Corps. I think all the other branches have them, no reason the USCG should feel they can't wear them if desired.
On the subject, I saw something the other day that made me think of how dangerous it can be in a combat zone....some servicemen wearing one tag around their neck and the other in their boot laces since they said you never know which end they will find and have to ID.
I was issued mine while assigned to PSU-305. As for the dog tag in the boot, when I deployed to Egypt, CENTCOM standing orders required us to lace one in the left boot.