Unusual, strong odors such as cat urine, ether, ammonia, acetone or other strong chemical smells.
Stange ventilation. This may include open windows on a cold day or other seemingly inappropriate time. There may also be fans or blower systems blowing air out of the structure.
Blacked out or completely covered windows. Windows may be blacked out with paint or covered with aluminum foil, plywood, sheets, blankets, or anything else that prevents other from looking in.
Excessive trash including large amounts of items such as antifreeze containers, lantern fuel cans, red chemically stained coffee filters, drain cleaner and duct tape.
Unusual amounts of clear glass containers being brought into the home.
Secretive / protective area surrounding the residence. This could include video cameras, alarm systems, guard dogs, reinforced doors, electrified fencing, etc.
Persons exiting the structure to smoke. They do this due to the flammability of the meth cooking process.
Little or no mail, furniture, visible trash and no newspaper delivery. This usually occurs when the residence is being used strictly as a cook site.
Lots of traffic. people coming and going at unusual times. There may be little traffic during the day, but at night the activity increases dramatically.
Rock salt in an unusual place such as a bedroom or bathroom.
Propane bottles with blue or green valves.
Rust on door hinges, keys, cabinet knobs, light fixtures, etc.
Stripped match books/striker plates.
Renters who pay their landlords in cash.