'Graffiti' is a term that has come to be used to mean any drawing/writing in public, no matter what its true meaning. So, there is then the distinction between that applied with, and without, permission. Without permission is vandalism, by definition, usually accompanied by trespass. Perhaps a suitable term would be, say, 'gravandalism'?! I'm only partly joking here - at least this language evolution would have a purpose, rather than the many which don't.
Trespass on the railway is inevitable, and the results will be varied. Despite the UK's railway fencing regime, it will always be easy to gain access via platform ends, level crossings, etc. The issue won't go away, just as youthful rebelliousness will never go away. If it's accepted that the activity will occur, then the only cost-effective course must be to charge those caught (a small fraction of the total) the full cost of the damage, which must either come from the individuals, their parents/guardians/family, and/or be paid over time. Of course, slapping a semi-permanent financial burden on someone is unlikely to shift their attitude to one of social angel, and will probably only harden their resolve.
In short, there is no solution with anything like our current societal framework, but the martyrdom achieved by the perpetrators and any sympathy garnered in the media are simply fuel to the fire.
