Many implements used today for graffiti vandalism can contain an acid which etches glass like the photo.
This form of graffiti is very destructive and cannot be cleaned off by a chemical cleaning method because the etched glass turns white where the graffiti is applied.

This type of vandalisim is commonly used on shop fronts and it can only be repaired by having the etched marks polished out of the glass. If this is unsuccessful then the glass must be replaced. Polishing is only successful if the etching is shallow as there is a limit to how much grinding and polishing the glass can sustain before it is distorted and weakened.

Caution needs to be exercised to ensure the glass is not made too thin and structurally weakened beyond the requirements of the appropriate Australian Standards. The other problem that can occur is a concave dip forming in the glass causing a distortion when you look through it.
The grinding and polishing of glass is a slow process, however replacing a shop front window can be very expensive. We have had several very successful clients sites where we have been able to repair the glass saving our clients quite a bit of money. So if you should ever have this problem you now know who to call!