It is a shame but white or light paints on building sometimes people interpret as an invitation "to come and draw something" using graffiti like in western countries or coal there is nothing else. It is like a canvas for artists.
In my home city there was a building that had a big light colored wall without windows and almost every week it was a horrible graffiti work was left, so the owners painted it every week. One day they decided to ask a well know among graffiti users artist to do a nice work of him on that wall, of course he left his signature under and it was really a great artistic work. You can't that wall never was spoiled again.
So that might be a decision for such buildings too.
That is a great job you, guys have done, before and after photos are really impressive. We need to involve more people in such projects.
I believe that in the past our ancestor also had to deal with such naughty young people who liked to leave their traces on walls. This is just very human.
Thanks for your educating post and wish you a nice weekend @onceuponatime