The appeal of the ion-impantation graffiti would be both the beauty of the shimmering and translucent colour, and the shear impracticality. Another advantage would be the permanence since the graffiti forms part of the surface rather than a mere coating.

The problems encountered by the artist would include:
hauling the ion-implanter and power source;
finding and cleaning suitable flat surfaces (glass and polished metal would be best);
leaving the ion-implanter in place for several hours (so that sufficient ions are implanted).