Like notaries, witnesses aren't generally required in order for a contract to be legally enforceable. However, each state may require special kinds of contracts (e.g., real estate deals, wills, and marriage agreements) to be witnessed by a third party in order to be binding.
McDonald's, apparently, use red and yellow because red=fast and yellow=hunger (hence fast food!). Remember also that meaning is what we create. It does not exist in the color itself and individual meanings may or may not exist in different cultures and individuals.
The colors indicate the speed of traffic on the road. 1  Green means there are no traffic delays. 2  Orange means there's a medium amount of traffic. 3  Red means there are traffic delays. The more red, the slower the speed of traffic on the road.