After one quick and simple prod via their website, the ANZ have cleaned up the rear of their bank branch on Great North Road.
My assumption is that parking spots like these would be reserved for the branch manager and other senior staff. Now that the fact that their site gets tagged has been drawn to their attention, I'd hope that they'll keep an eye out for it when parking their car in future, and will take action without me having to give them a poke.
I also noticed that the law firm next door has cleaned up their back wall - that means that we've gone from 100% of the businesses in this particular spot being vandalised to 80%. A start, but a long way to go.