I believe to be the case because of the simple common courtesy and the golden rule effect. The function of the receiver is to finish the communication exchange. This completion should eliminate hard-feeling. There are other methods mentioned, but I do not think they are feasible nor do I think they are easy to use while driving, for example the flash cards, or technological communication devices like phones and CB's. The so-called universal communication gestures like waves, etc. should be taught by example.
People learn by modeling.
If we ourselves begin to implement these gestures, so we have a community of drivers modeling. Another way these methods of gesturing could be taught is through Quality Driving Circles. The conclusion is if there is to be any UPC then we must start it now and teach, and channel it to every area of driving. The usefulness of these gestures could prevent some bad vibes between drivers who are courteous and expect to be acknowledged. There is nothing wrong with this expectation.