Abstract: A pivotally mounted flag assembly for use with rural type mail boxes to automatically indicate that a pivotally mounted door of the box has been opened. The door pivotally mounts one end of a relatively stiff wire, the opposite end of which penetrates an oppositely disposed vertical wall of the box to engage a weighted semaphore type signal, the release of which causes the signal to rotate under the force of gravity to expose a free end thereof above the mail box where it may be viewed from a distance.