Signal

The speed of a vehicle can be a signal of how fast it's going.

The warning signal sounded when the tornado approached.

The traffic signal turned red, indicating we had to stop.

The loud explosion was a signal that something had gone terribly wrong.

The cough was a signal that she was not feeling well.

The smoke coming from the engine was a signal that the car needed to be checked.

The teacher raised her hand as a signal for the students to quiet down.

The dark clouds were a signal that it was going to rain soon.

The alarm was a signal that the building was on fire.

The tremors were a signal that an earthquake was coming.

The wireless router in the house emits a strong Wi-Fi signal.

The sound signal indicated a malfunction in the system.