Who tagged the Children’s mural?

One remnant of the Children’s Village at St. Joseph’s that’s been preserved is the mural on the side of the building facing Tenth Street. The mural was recently defaced with graffiti. Presidio Knolls Schools currently runs a Mardarin immersion program at the site. School officials have tried all the usual remedies to remove the tag but it’s a metallic paint which resists most solvents.

I own a print shop and have chemicals here that would remove just about anything but I would worry about what might happen to the adhesive holding the ceramic tiles in place. Is there anyone out there with expertise in a situation like this? Whoever comes up with a solution will be a hero to a lot of kids.