Yesterday I was returning to our nice flat in a very run-down part of Naples near Garibaldi Square, after half a day at the Naples National Archaeology Museum. I decided to detour to Montesanto on the subway line, because my map showed some nice palaces there. This detour was a damp squid because the palaces had disappeared centuries ago, although the names stayed there.
I eventually got to the right platform on Montesanto for the trip home, packed with waiting commuters as it was about 5pm and the subway trains are not at all frequent, e.g. every 20 minutes. The platforms both sides were in clean condition, but unusually, youths were using my platform edge as seating, dangling their legs above the tracks. After a while one of them, about 18-20 with red hair, pale skin, a New York University sweater and baggy pants, got up and joined two mates. One was thin but very tall, the other swarthy and clad in pseudo camouflage top.
They were all only a metre or two from me. The redhead was clutching some tubes, about half the size of a runner's baton. One tube was giving him trouble and he was trying to do something with the lid. I noticed a wad of cotton fall to the platform and he put it back in the tube (I had initially thought there was something edible in the tubes).
I was standing against the light green perspex/glassy wall of the station. There were dozens of others alongside me, some standing and others filling seats against the wall. Still struggling with the cap, the redhead moved to a rubbish bin 50cms from me and ground the top of the tube against it. He looked pleased when something blue came out of the tube onto the rail of the bin. He took two steps towards the wall, between the bin and the first row of seated men and women commuters.  This was a wall gap of only a metre.
With practised movements, he waved his arm at the wall (I couldn't quite see what he was doing), stepped back, admired the wall, and took a few steps left to rejoin his two friends.  They all seemed quite merry and animated.
Someone moved and I could see the wall. On it now -- it was previously pristine for the whole length of the platform -- was one of those mindless 'tags', the scribbled letters P, W and C, in a squiggly pattern about half a metre square.
I now saw that at least two of the three youths were carrying handfuls of these tubes, king-sized textas. The swarthy youth had a red, blue and empty tube, and the redhead had his own bunch. They were making no attempt to conceal them. I wondered what function these tubes had, other than for graffitists.
I looked at the commuters to see how they were reacting to the wall being defaced at peak-hour right next to them. They would all be fully aware of what had happened but they studiously minded their own business, and acted as though the trio of graffitists was invisible. Surely, I thought, some of those studying their smartphone's would tap out an alert to the station police? Obviously this wasn't happening.
The trio were clearly on their graffiti mission. I'd say they'd been active for an hour or two.
At that moment the train arrived and those still sitting on the platform edge pulled their legs up.
I found myself sandwiched among the three youths as we boarded. Thankfully they moved down-carriage a bit. From there they kept up a loud banter. I tried unsuccessfully to work out from their talk if they were native Napoli citizens or some outsider group. I did make out some variant on 'chi uccede' - croaker, killer, zaps or some other unpleasant jargon. 
When I stood up to get out at Central Station, once again I was sandwiched among the trio. They ignored me and formed a knot in the crowds heading for the stairs.
Even now, at Naples main train station, they flourished their graffiti tools of trade in their hands. They moved purposefully, I guessed to some other line where they would continue their evening's fun. Whatever police or officialdom was present, the trio obviously had no fear of them.
I wonder about it all. They did not seem particularly tough or threatening. That's not to say the other train-goers weren't intimidated by them: who knows what else besides giant textas they were armed with? Or were train-goers utterly indifferent to vandalism on their subway, in broad daylight among crowds?
Melbourne has its train graffiti vandals too, painting their horrid tags on platforms and carriages and rigorously scratching train windows into an opaque mess. I recall a case a year or two ago where three were caught and prosecuted -- they had come from Adelaide on a spree and in a week or two, had vandalised hundreds of places on our train system. They had operated late at night.
Let's hope Melbourne never gets to the pass where graffiti vandals do their work openly.