After a week of looking at it every time I went past, I reported it to the local area manager. It was fixed the next day.
But here is what I discovered about Police management. Stations like this one, which are only staffed part time, no longer appear to have anyone in charge of them. The Police hierarchy may dispute that, but I walked into the station one day to report a different problem and asked to see the Station Commander. The response from the Constable behind the counter was "We don't have one".
So I asked to see the Officer in Charge (who might be a Sergeant or Senior Constable). Same response - they didn't have one. When I asked who was in charge that day, he looked around at the gaggle of Probationary Constables that were sitting around drinking cups of tea, and shrugged his shoulders.
So you can't assume that graffiti will be noticed by the Police, and any action taken by them. They sometimes don't even lift a finger when their own premises are hit.
I also found out something else - stations like this are now maintained by contractors. There are no internal maintenance staff, like painters and plumbers, left in the administration wing of the Police Force. So the poor old cops can't just pick up the phone anymore and dial someone in maintenance and get them to pop around with a tin of paint and a rag to fix things. It has to go through a Contract Manager, who contacts the contractor, who may or may not do the work (depending on whether they have been paid recently).
In each Command (LAC, or Local Area Command) there appears to be a LAM, or Local Area Manager, who is responsible for dealing with this administrative type stuff. All you have to do is look up the White Pages, call your nearest Police Station and ask to be put through to the LAM. If they have no idea what you are talking about, ask to talk to the LAC - that's the big chief in the area. They should know who that is, and should get in a panic if you ask to talk to them. Five Dock is an offshoot of Burwood Station, which is the main station for this area, and the LAM works out of Burwood. This might be the same in other areas, where there is a main station and some satellite stations around it.
I found that the Burwood LAM was very responsive once she knew about the problem, but until I rang and reported it, no one had let her know!
Like I keep on saying, the Police working from this station either failed to notice the vandalism, or they did and figured that "somebody else" would take care of it. The same old story - somebody else's problem.
Took me about 2 minutes to get it fixed.