Likely as functional as the drug free zones, the smoke free zones, the gun free zones and ect. Looks good to those who obey the law, lame as shit on your shoe for others and does nothing but stink.
Sounds like a stupid idea created by the same hoity-toity fucks who try to push their smoking bans on people.
How does one go about creating gang free zones? Do you mean zero tolerance for gang activity or affiliation? It would be funny to see them attempt this here..