In the weeks after Katrina there were several stories about neighborhood defense groups.
One story described a bunch of guys who were armed and serious, and had done things like rigging beer can “alarms” on the front porches on their block. The guys described one daytime encounter which had turned out very badly for the perpatrators.
And there also was the widely circulated photo of another group, showing about 20 middle-class neighborhood guys with their hardware and a huge warning sign telling looters to stay out or else. One would imagine that neighborhood stayed pretty safe.
I saw a sign that simply said... “You loot we shoot.”