On a busy street, at least a block or so before the turn. On a less busy street, not a block perhaps but certainly some distance before the turn.
When turning you should signal during the last 100 feet before a stop sign. This is courteous to all drivers around you.
100ft
100 ft
10 feet.
100feet
100 yards
In any state you should signal within 100ft of turning but, to be safe you should always signal. Because you never know whats going to happen.
100 ft
About 100 feet.
Before turning left, the driver should signal, check for oncoming traffic, yield to pedestrians, and make sure it is safe to proceed.
100 feet
At least 500 feet.