Which of the following is a visual sign that indicates a minefield?

A visual sign that indicates a minefield is typically a warning sign or buoy. These are specifically designed to alert individuals to the presence of mines and generally feature recognizable symbols or messages indicating danger. Such warnings are crucial for ensuring the safety of people in the vicinity, especially in areas where mines may not be immediately visible or where terrain may obscure them.

While landmarks and geological features can aid in navigation, they do not inherently signify the presence of a minefield. Brightly colored flags might be used in military operations or to mark specific locations, but they are not standardized indicators of minefields. Checkpoints manned by soldiers can imply caution in an area, but they are not direct indicators of mines. Therefore, the use of warning signs or buoys as visual indicators of a minefield is the most definitive and universally understood method for denoting danger in these zones.