Abstract: An elongated rod, having a signal flag on one end thereof, is secured by its other end to a housing adapted to be rotatably secured to the side of a rural mailbox adjacent its entrance end, the mailbox having a vertically swinging hinged door for opening and closing the entrance. The housing is provided with a radially extending latch arm releaseably engageable with a cam secured to the adjacent side edge of the door. The housing contains a coil spring for rotating the housing from a horizontally disposed position of the rod, when in a first cocked position, to an upstanding signaling second position, when the door is opened.