Originally Posted by
mnemia
One thing that I find just as useful as signalling my turns is using "instructional" gestures on motorists who seem confused or indecisive about what to do around me. For example, I'll sometimes gesture with the "come" gesture if they have the right-of-way and seem reluctant to claim it (as a way of acknowledging that I see them and plan to yield).
One problem with giving other drivers instructions ("waving them on", for example) is that they may assume that it's safe to follow them when it isn't. It may be safer to indicate what you are doing and let the driver drive his own car (rather than you doing that for them).