C. Read again and write T for True, F for False or NM for Not Mentioned. 1. Smoke signals are made when you throw water over a fire. 2. A smoke signal is only used to communicate that danger is close by. 3. Pigeons carried messages on their backs. 4. After World War II, people stopped using pigeons. 5. Semaphore flags were used a lot during the 1800s. 6. Electricity was needed to send a message by telegraph.