Which signals may be used to warn of a stopped vehicle that contains explosives?

The use of reflective triangles as a warning signal for a stopped vehicle containing explosives is appropriate due to their visibility and regulatory acceptance. Reflective triangles are specifically designed for road safety and are required by federal regulations for use as a warning signal when a vehicle is disabled or stopped unexpectedly. Their bright, reflective nature helps ensure they are visible to approaching traffic from a distance, allowing drivers to take precautionary measures.

While flares or fuses may seem like a logical warning signal due to their visibility, they can pose a significant safety risk when used with vehicles carrying explosives. The same applies to signal fires; while they could theoretically attract attention, they also present a fire hazard that could trigger explosives. Therefore, the most suitable and safest option for signaling a stopped vehicle that contains explosives is the use of reflective triangles.