Final answer:
The red flag historically symbolized a readiness to battle, defiance, and revolutionary spirit, as seen during the French Revolution and later with the Russian communists.
Step-by-step explanation:
The sailing of a red flag historically signaled a number of sentiments, depending on the period and context. Dating back to the 13th century, a red streamer, or 'baucans', flown from the masthead of a ship, was an indication of an intention to give battle and fight to the death. Later, in the 17th century, a red flag came to symbolize defiance and the intention to resist.
During significant events such as the French Revolution, the red flag was associated with the revolutionary spirit of the common people, representing the blood of the martyrs and the collective willingness to sacrifice for the cause. The red color also related to symbols of the revolution, such as the Phrygian cap. Subsequently, the red flag was adopted by the Russian communists as a symbol of their movement and became the national flag with the addition of the yellow hammer and sickle after the Bolsheviks' rise to power.
In all cases, the red flag serves as a potent symbol representing an attitude of defiance, a revolutionary spirit, and a readiness to engage in battle and endure sacrifices for a cause or movement.