Final answer:
A black and white sign with an arrow signifies a mandatory turn in the direction the arrow points, used to guide traffic flow and prepare drivers for turns or merges.
Step-by-step explanation:
A black and white sign with an arrow pointing to the left or right generally indicates a directional instruction in traffic regulations. When you see such a sign on the road, it's important to prepare for a mandatory turn in the direction of the arrow. If the arrow points to the left, you must turn left; if it points to the right, you must turn right. These signs help in maintaining traffic flow and ensuring drivers are prepared for upcoming turns or lane merges.