I thought that the fad of spraying the sides of trains had passed, but I too have noticed a recent revival of it, including on some brand-new SWR 707s. I agree with those above who feel that it produces a bad impression.
There are some lads who can produce quite nice images with a paint-spray: they should be encouraged by suitable means (not excluding prosecution) not to do it on trains, stations or other public utilities and also provided with some officially-sanctioned place where they may exhibit their talent without causing bother. Those who merely spray crudely-drawn initials should be punished via fines and given some useful task, such as cleaning up what they and others have done with paint-sprays.