It is everywhere.
It doesn't matter where you go. If there is a blank and reasonably smooth surface - an old shed, under the bridge, on garden seats - it is possible canvas for self-appointed graffiti artists. No real skill is required, as V pointed out, they all seem to follow a similar style. The graffiti usually consists of words in fat bubble letters, just as what we saw on the Mrt train graffiti. The repertoire of the graffiti artist might even extent to simple cartoon characters. Some sadly resorted to random squiggles of paint.
And thus, in the otherwise pristine environment of pastoral countryside, in the gleaming towns, a subculture of free-spirited self-expression insists on making its presence felt, or rather, seen.
Graffiti is so prevalent in Switzerland that I am beginning to wonder if the recent case of Mrt vandalism is reflection more of cultural differences than criminal intention. Maybe it is perfectly acceptable over there, and even blotches of spray paint are preferred to unadorned surfaces.