I wasn't quite sure if I wanted to get into this one. Because everyone is going to interpret this improperly. You should give hand signals. The signals were actaully designed for vehicles that do not have mechanical turn signals. Under the law here in Arizona a vehicle is any means of transportation that utilizes the roadway's in a short form (that includes bikes).
Here is what is prescribed by law in Arizona:
28-756. Method of giving hand and arm signals: A. Except as provided by subsection B, a person shall give all hand and arm signals required by this article from the left side of the vehicle in the following manner, and the signals shall indicate as follows: 1. Left turn. Hand and arm extended horizontally. 2. Right turn. Hand and arm extended upward. 3. Stop or decrease speed. Hand and arm extended downward. B. A person operating a bicycle may give a right turn signal by extending the right hand and arm horizontally to the right side of the bicycle.
Note it does specifically make mention of cyclists and an exception to the actual manner in which to make a right hand turn signal.