- An unusually large amount of traffic coming to the building - in cars, taxis, or walking - often at strange hours. Visitors may sometimes pound on doors or shout to be let in. This traffic is usually quick with people staying only a short time. Sometimes they don't go in at all; instead, someone comes out to meet them.
- Finding drugs or drug paraphernalia (syringes, pipes, etc.) in the area.
- Repeated, observable exchanges of items, especially where money is visible.
- Offers to sell you drugs, or conversations about drugs that you overhear.
- Noxious odors from or around the buildings, such as "musty" smells.
- Buildings where extreme security measures seem to be taken.
- Buildings where no owner or primary renter is apparent, and no home activities, yard work, painting / maintenance, etc., seem to go on.
- Many communities have unpopular residents. But obnoxious or peculiar behavior, or a different lifestyle, racial or ethnic background, or economic level doesn't necessarily mean the person is a drug dealer.