This question tests the understanding of basic road signs used in Ontario, Canada, particularly the sign indicating slow traffic on multi-lane roads must keep to the right. This is a fundamental traffic regulation under the Ontario Highway Traffic Act, often encountered in real-world driving situations on multi-lane roads where traffic is expected to flow efficiently. In actual driving, recognizing and adhering to this sign is crucial for maintaining smooth traffic flow and ensuring safety on highways and major roads. The Ontario Highway Traffic Act specifies that slower-moving vehicles should use the right-most lane to avoid obstructing faster traffic, which is a common practice to facilitate efficient road use.