I asked before if it was bare masonry. That is painted masonry. Big difference Terry. I could be wrong, but I have never encountered masonry that is colored like that out of the factory. 99% chance the wall is painted with a latex product. If so, even without Taginator the paint will come off. No way are you going to get the area of paint the City painted over the graffiti and keep the existing color coat intact.
From that picture you posted, looks like the overcoat paint is already lifting, or the undercoat, or maybe the masonry is in bad shape underneath.
I owned a painting company in Chicago for many years. From the looks of it the overcoat of paint and any other paint that is failing needs to be removed (15 degree tip should work, no chemicals), wall allowed to completely dry (maybe 48 hours, depending on the weather, humidity, ect) primed then repainted.