There was even graffiti in that alley in the city that the android girl was at. Does this mean there are gangs in the future? If so, whatever happened to crime and deviance being basically eliminated in the 24th century?
It was artistic expression, of course.

And, honestly, even today graffiti is hardly the sole province of gangs. I'm sure they have rebellious teenagers and avant-garde street artists in the future.

It's interesting that Dahj was hiding there. Seems to hint that the district actually was simply kept this way for historical and cultural reasons and nobody actually lives there, as possibly hinted at by showing the empty streets...