Identify the NATO NBC defense sign for Biological hazards.

The correct sign for indicating biological hazards in a NATO NBC (Nuclear, Biological, Chemical) defense context is characterized by the use of a color scheme that effectively communicates the danger. The sign for biological hazards is specifically colored blue with red letters. This combination is intentional as it helps to draw attention to the sign, ensuring it is noticed quickly in a high-stress environment which is often relevant during biological threat conditions.

The blue color stands out to personnel, while the red letters serve to emphasize the warning text, facilitating rapid recognition and comprehension of the hazard type. The distinct visual contrast between blue and red helps personnel identify the risks associated with biological agents efficiently.

Using other color combinations, such as yellow with black letters, white with red letters, or red with white letters, lacks the established NATO standards for biological hazard identification. Each of these variations corresponds to different hazards or categories, which are crucial for ensuring that personnel respond appropriately to specific threats.