Without commenting on the way poor neighborhoods stay poor (in many meanings of the word) because of crime, I've noticed a significant step forward in this regard.
Standard folding iron gates that usually protect storefronts in bad neighborhoods are commonly ugly and bad for business. They yell out 'danger.' But they are necessary to protect the business. Windows etched with battery acid or broken are very expensive to replace and equally expensive in loss of customers when not replaced.
The photo on the right shows a wonderful solution. The protective wall is steel mail painted black. It protects beautifully and to my eye it is esthetically pleasing.