Let me tell what I witnessed yesterday which is why I posted.
Coming through MK I saw a team of cleaners out trying to remove graffiti from glass bus shelters using some kind of rotary buffer/grinder.
This removed the graffiti (of sorts) but left the shelters in a awful state with large areas of etching, the graffiti would, if left alone have looked better. :
Alex, would your solution work on glass?