Let's say your a drug addict but don't happen to have anything on you, they look you up and your background has prior arrest for drugs. Maybe you look like your on drugs and have all the tell tale signs. In this case your gonna go to jail.

What if you're a tourist or someone who got lost trying to go to find Ikea. They would hassle you and most likely give you a lecture then lead you out of the area.

These types of areas have signs. If you are interested why they have such areas watch Snow on the Bluff, it's a very accurate depiction.