they are easy to remove (not cheap) so actually in the keynesian model they represent both the construction process of new infrastructure, then the tearing down process at end of usefulness. women pay sometimes tens of thousands of dollars to doodle themselves up, then another tens of thousands to erase it. at the end of the day it's some poor sob's money she's infusing the economy with exactly like every other form of affectation spending such as clothing, accessories, cosmetics, etc.
Canada