1. Such regulation would be virtually unenforceable. It would be a waste of time. The police have more important things to do than look out for the few drivers that sign. How will they know it is signing, or just someone who uses their hands alot when talking?
2. Unless you can demonstrate that crashes due to signing are commonplace, there is no reason to regulate it. Can you or anyone cite some relevant statistics or facts, showing the need for regulation of SWD?
Why are we so regulation happy? Regulation should only be used when absolutely necessary. Signing while driving does not appear to need regulating. Regulating SWD will be unlikely to save many lives, if any. You may like telling others how to live, but they will naturally resist such regulating.