Which of the following is part of the equipment or procedures used to protect a work site?

High-level flags are indeed a critical component of equipment or procedures used to protect a work site. Their primary function is to enhance visibility and alert individuals about specific site conditions or hazards, particularly in environments where heavy machinery is in use or where there may be other dangers present. They serve as a visual warning, helping to ensure that everyone on or near the work site is aware of potential risks, which is an essential aspect of maintaining safety.

The other options, while they have their roles, do not directly pertain to safety in the same immediate sense as high-level flags. Large machinery is a part of the work site itself, but it does not serve a protective function. No parking signs help manage traffic and parking but do not directly protect the site from hazards. Standardized uniforms are important for identification and professionalism but do not inherently protect the site. High-level flags stand out as specifically designed to signify caution and ensure the safety of personnel and operations around potentially dangerous areas.