In April 2017 a number of Greek artists painted graffiti around 4th Infantry Regiment Square in Piraeus http://www.athina984.gr/2017/04/07/mia-platia-gemati-minymata-allilengyis/

I believe this piece is done by an artist called River, I am not 100% sure so have marked it as artist Unknown also I do not have the exact location in the square for all the pieces.