#1: large amounts of light escaping from open doors/windows.... prighty obvious..
#2: "Blacked out" portions of the house. AKA all windows to one large room completly blacked out
#3: Smell, this is a big one.... i live in a place where cops walk through some neighbourhoods with their drug dogs. even an "off-duty" cop can call it in to his buddys....
#4: power consumption. hard to get away from and its a BAD idea to try and steal power. that gets you more trouble than growing alot of the time.....
there are some things that you cant get away from. in vancouver they do regular "sweeps" with a gamma ray scanner (dont know how it works, but it does... has since the 60's..) and they have been busting alot of large grows because of it.
the best advice i can give is to keep it to yourself. its common sense but i know alot of people who have talked and been busted for it.
just dont give them probable cause!