Hand signals are a good thing, generally I look for at least 2 signs that a person on the road is signaling their intensions...be it turn signal and hand signal or tune signal and front wheel initiating turn before I consider a signal valid.
Two many times, only one signal given may be a false alarm or improperly given for something else the rider/driver intends to do. Example... left turn only, but does a U-turn in front of you AND on coming traffic instead!