Spoil grounds, anchorage, cable areas, and military exercise areas are marked by yellow buoys. What special mark on the buoy will indicate the specific area you are in?

Yellow buoys serve as special marks indicating designated areas such as spoil grounds, anchorages, cable areas, and military exercise zones. The use of specific markings on these buoys enhances navigational safety by clearly identifying the purpose of the area.

The option that states "lettering on the buoy" is correct because it provides crucial information specific to the marked area. This lettering can convey the name of the area or additional instructions pertinent to navigation, helping mariners understand restrictions or guidelines associated with that particular space.

While other markings like top marks and shapes could be indicative of buoy types, they do not directly provide the detailed information necessary for understanding the nature of the area marked by a yellow buoy. For example, topmarks like triangles or spheres might indicate the buoy's function in general navigation but won't specify the exact nature of the designated area. Similarly, a topmark consisting of two cones with points up is often used for navigational aids but does not carry specific information about spoil grounds or military zones. Therefore, lettering on the buoy is the most effective means of indicating the specific area and its associated requirements.