Which of the following is NOT a regulatory sign?

Regulatory signs are designed to inform drivers of specific laws and regulations that must be followed. They are mandatory and have the force of law. Examples include signs that indicate prohibitions (like "Do not enter" and "Do not pass") or directions that must be observed (like "Keep right of the divider").

The sign indicating "Merging traffic ahead" is a warning sign rather than a regulatory sign. It alerts drivers to potential changes in traffic conditions, but it does not impose a specific legal requirement like yielding or stopping. Instead, it serves to prepare drivers to adjust their speed and positioning because of the possibility of other vehicles entering their path. Therefore, it does not fit into the category of regulatory signs, making it the correct answer to the question.