Graffiti treaty

This is our garage door.  No matter where you live, “good” neighborhood, “bad” neighborhood, if you have a garage door or a shop shutter, or an empty wall sometime in the middle of the night, someone will leave their mark on it.

People tell me that the only way to stop graffiti is do your own.  I guess the government and police have kind of given up the fight.  Putting up your own, earns graffiti respect and the right to be left untouched.  So I headed out to Gracia before opening hours to see it it was true.   On shop grates yes, anywhere else no?