That, I believe, stretches credulity a bit - you're telling me that in the thousands of years since the Usurpation, in which Sidereals, Terrestrials, and the rare handful of Solars that popped up from time to time each had their own separate interaction with Lunars, none of them ever made the observation, "Hey, these Lunar guys suddenly have glowing metal tattoos - could they possibly have some sort of beneficial effect attached to them?"
Who said they'd have to be silver?
All the more reason for the Sidereals to steal the technology and put it to use.
For Solaroids or Terrestrials, the solution is easy - make your own "hide the tattoos" Charm.
For Sidereals, well, that would literally never come up if yours was the sort to spend all his time in Yu-Shan.
That's what I thought.