What does a circular yellow sign typically mean?

Answer: C — Advance warning of a railroad crossing

A circular yellow sign is used specifically to indicate an advance warning of a railroad crossing. These signs alert drivers to the potential presence of trains and encourage them to approach the intersection with caution. The circular shape of the sign is significant; it differentiates railway warnings from other types of road signs. In contrast, stop signs are typically octagonal in shape, while yield signs are usually triangular. Additionally, construction zone signs often use orange and are rectangular or diamond-shaped, rather than circular. Understanding these shapes and their meanings is crucial for safe driving and recognition of road hazards.