One method of putting graffiti on glass is using acid. A marker filled with acid will be used to write on the glass. The acid will dissolve the glass.
Acid etching cannot be removed the same as paint because the actual surface of the glass is etched and modified. The only way to remove the acid etching is to sand the glass just like removing a scratch to get below the damage to the glass. After an undamaged portion of the glass is now exposed, the pre-polish and final polish stages can then be completed.
Glass that has been intentionally etched can also be completely resurfaced for a distortion-free and clear view.