Identify the symbol used for an isolated danger mark.

• A. Two cones up
• B. Magenta flash symbol
• C. Black and red, two black spheres
• D. Yellow cautionary area

Answer: (C)

An isolated danger mark is marked with red and black horizontal bands and has a topmark of two black spheres. This symbol identifies a specific hazard that is isolated from the surrounding water, so mariners should keep well clear of the danger and pass at a safe distance around it. The red/black color combination is chosen for high visibility against the water, making the hazard easily recognizable in different lighting and sea states.

Two cones up corresponds to a different mark used to indicate a safe direction or channel, not an isolated danger. A magenta flash symbol points to a special mark with a magenta light, which serves a different purpose, and yellow cautionary area marks signal general caution rather than a specific isolated hazard.