A sharply divided Milwaukee Common Council passed a new anti-gang loitering ordinance which essentially empowers the cops to order "known" gang members to disperse. Alders Michael Murphy and Ashanti Hamilton denounced the new law as "pandering" and "meaningless."
A recent article in the National Law Journal (I'd link but you need a subscription) discusses a related phenomenom, civil injunctions prohibiting gang members from congregating in specified zones (normally the gang's presumed "turf.") The injunctions (and ordinances like Milwaukee's) are not without legal problems (they can be, but are not always, constitutional), but law enforcement authorities do cite significant crime reductions as a result of the injunctions - at least within the protected zones. If nothing else, they reduce the feeling of law abiding residents that they are living in an occupied zone.