Graffiti could be a form of art expression, but in Athens most of these are nothing but vandalism to public properties.
Graffiti are often seen on road signs thus blocking some words giving directions, or on bus / metro train’s seats, or its glass windows or doors. In the case of glass surface, the glass is usually scratched with some sharp object.
I have visited many European cities (Edinburgh, Amsterdam, Düsseldorf, Vienna, Milan, Prague, Bucharest), but only in Athens I found road signs been covered up by graffiti. Maybe the other cities do have some graffiti but are not so frequent like in Athens to be noticeable?
I hope the city of Athens impose heavy fines when one is caught for vandalism before the situation becomes worse.
The photo was taken on the metro train (subway).