I wouldn't have thought so, but I had an experience on my way to work this week that made me wonder. I was on a narrow 2 lane road (which I take for about 1/4 mile), approaching a right turn where I turn to go about 100 yards over to the main road. I have to take the lane for this stretch, and had several cars pass me properly, but just after I signaled to go right I had a JAM go into the left lane to go around me, and then turn right into the left lane of the destination road while I was turning - I yelled at him but couldn't even see inside due to his illegally dark tinted windows. (If I'd have had something to throw I might well have done it)
I can assume (perhaps wrongly) that he wouldn't have pulled this if I hadn't signalled, but it made me wonder. In the absence of traffic ahead which might need to know, might it be best to just make your right without letting the JAM's behind know?