I'm no expert but from what I've learned graffiti all over the place means gangs. Gangs mark their 'Turf" with graffiti to warn other gangs to back off we are here. After some study by walking around I've marked down streets and aves where there is likley gang activity.

28th Street going east and west starting at Carlton High School and ending where the safeway is.
Central Ave. To the North end of the Correctional Facility. High activity there. (if you still don't know it's those apartment looking buildings across from kinsmen water park)
Someone has also told me that there is gang activity on 13th Street west.
I've also noticed some activity going around St. Marks church.
In the heart of Central Ave. Probably but not likley due to all of the people around. But you better watch your wallet.
Possibly where the welcome Inn is too.
And now I'm not sure of this but 16th, 15, 14th, and 13th Streets there may be activity there. (all the to west where the Bernice Sayese Center is located.

I say pretty much this whole city is filled with gangs, one day you could be walking your little poodle down the road then all of the sudden you have a rock the size of a pop corn bag fully popped at your head and to be mugged and have your dog either beaten really badly or stolen.
I've heard a story where a little boy and his friends were out playing in a baseball field where that old public school used to be near Welcom Inn and a huge mob of kids were running down the alley at full speed. Then an older woman came running up thinking that this boy and his friends were the ones who did it. The friends asked what and the woman said throwing rocks at her baby that was just playing on her lawn. I'm guessing this happened on 8th Ave. After some talk the woman found out that these were not the kids that did it.
(end of the story)

I suggest that if Police Officers see a large group of kids in a back alley or just walking down a street they should pull up and ask what's up. No getting out yelling get on the ground but just to ask.
People say it wont do much for the police to just drive up and ask what's up. But I think if it's done the kids or gangs will start to think the police are stepping it up and may also think that the police are on to them.

Not in PA?

Gangs?! Come On! What Your Seeing May Be Minimal "Gang" Tags. What the Real Problem Is. Kids. Kids Finding Old Spray Cans Or Just Out For A Laugh, Passing By On Way To Wherever. Some Of The Material Out There Is 4 ft Off The Ground, Mis-Spelled Words, Swear Words, Squiggly Lines! Not Exactly "Gang" Tags. Words Of Advice...People Don't Leave Half A Can Of Fluorescent Marking Spray On Backside Of Your Garage. These Kids Doing This Certainly Don't Have The Time Or Cash To Buy A Can Of Spray Paint Just To Wreck Stuff.