What is the minimum height for letters on the "School Bus" signs?

The minimum height for letters on "School Bus" signs is 20 cm. This specification is in place to ensure the letters are clearly visible from a distance, enabling drivers and other road users to recognize the sign promptly, especially in potentially hazardous situations. This visibility is critical for safety as it alerts drivers to the presence of school buses, which transport children and may involve frequent stops.

Using properly sized letters on signage is part of broader safety and regulatory measures designed to protect pedestrians, particularly children, who are at greater risk near school zones. The focus on height standards reflects the need for legibility under various conditions, including different times of day and weather scenarios. Inaccurate sizing could lead to misunderstandings or missed signals, which could compromise safety. Adhering to the 20 cm requirement aligns with these safety principles, making it the correct answer.