Apparently it IS required if there are any vehicles that MIGHT be effected ... in other words, if there are any other vehicles in sight, you should probably use a signal.
28-754. Turning movements and required signals
A. A person shall not turn a vehicle at an intersection unless the vehicle is in proper position on the roadway as required in section 28-751, or turn a vehicle to enter a private road or driveway or otherwise turn a vehicle from a direct course or move right or left on a roadway unless and until the movement can be made with reasonable safety. A person shall not so turn any vehicle without giving an appropriate signal in the manner provided by this article in the event any other traffic may be affected by the movement.
B. A signal of intention to turn right or left when required shall be given continuously during not less than the last one hundred feet traveled by the vehicle before turning.
C. A person shall not stop or suddenly decrease the speed of a vehicle without first giving an appropriate signal in the manner provided by this article to the driver of any vehicle immediately to the rear when there is opportunity to give the signal.