Final answer:
A red octagon shaped sign universally signifies that motorists must stop. This shape and color combination is specifically associated with the 'stop' directive, differentiating it from other traffic-related signs.
Step-by-step explanation:
The message that will be found on a red octagon shaped sign is stop. This sign is a universal traffic sign used to inform drivers that they must come to a complete halt at an intersection, before proceeding when it is safe to do so. The other options provided -- do not enter and one way -- are different traffic directives with their own unique signs. For instance, a "do not enter" sign typically appears as a white rectangle with a red circle that has a horizontal white line through it. A "one way" sign is often a vertical rectangle with an arrow indicating the direction of allowed traffic.
The stop sign is utilized worldwide and is particularly recognizable due to its distinct shape and color, serving as a critical component in managing traffic safely and efficiently.