What is the name of the sign that directs trains to approach at a speed limit and is represented with a yellow background?

The correct choice highlights a specific sign used to indicate an approaching speed limit for trains. The name "Approach Speed Limit Sign" is designed to clearly communicate to train operators that they need to reduce their speed in preparation for what lies ahead, ensuring safety as trains enter areas where a lower speed is warranted.

The yellow background of the sign serves as a universally recognized warning color, emphasizing the importance of adhering to this speed restriction. This sign plays a critical role in maintaining safe operations on the rail network, as it provides essential information to train crews about the need to adjust their speed in advance of potential hazards or changes in track conditions.

In contrast, other options like the "Speed Limit Sign" are more general and do not specifically denote an approach to a speed limit, while the "Diverging Approach Speed Limit Sign" applies to situations involving diverging tracks rather than a general approach. The "Resume Speed Sign" indicates an increase in allowed speed but does not address the necessity of reducing speed upon approach to a restricted area, making it less applicable in this context.