Abstract: A mailbox having a door and a signal device to indicate that the door has been opened when a mail carrier puts mail in the mailbox. The signal is urged to and held in an erect position by a helical spring fixed to a side of the mailbox at one end and having a rigid staff inserted in the other end of the helical spring. The door is hinged to the mailbox at its bottom to swing from a vertical to a horizontal position. Cotter pins are provided to support the signal on the box and on the door. Each cotter pin has legs that extend through a hole in the mailbox and in the door. Each cotter pin has a ring on it that receives the signal. One of the cotter pins is attached to the door. When the door is opened the ring moves with the door and off the end of the staff thereby releasing the staff and allowing the helical spring to swing the staff to an erect position. A rectangular template is provided for forming holes in the mailbox and door for the cotter pins. A flag may be attached to the staff.