What shape is a non-lateral marker that warns of hazards?

A non-lateral marker that warns of hazards is represented by a diamond shape. This shape is widely recognized as indicating potential dangers or obstacles in the water, such as rocks, wrecks, or shallow areas. The diamond shape stands out and is easily identifiable by boaters, serving as a clear signal to exercise caution.

In the context of navigation signage, the use of different shapes conveys specific meanings. For instance, a square or rectangular shape typically conveys information or regulatory messages, while a triangle often indicates yield or caution in various contexts, such as road signs. A circle usually represents information or guidance rather than warnings about hazards. Therefore, the diamond shape is specifically designated for hazard warnings, making it the correct choice for this question.