There are many different warning signs for many different situations and, depending on the situation, they all have varied importance. For example, on the back of a truck you might see a sign that says it's slow or that it carries hazardous material. Both of these are important, but only one might be considered absolutely necessary. The slow-moving vehicle sign is to prevent road rage or confusion while the hazardous material sign warns people to be extra careful around it and, it something happens to the truck, to proceed with more caution than you would with a regular truck.
