Abstract: Subject device is automatically tripped by manually opening the door of the mailbox. The device includes a frame which is intended to be attached to the lower edge of the mailbox. Pivotally attached to the frame is a signalstaff adapted for pivotal movement between an upright position and a recumbent cocked position. Attached to the upper end of the signalstaff is an omnidirectional signalhead which provides conspicuous evidence from any angle of view that the door of the mailbox has been opened. The signalstaff is held in the cocked position and/or selectively released therefrom by a novel trigger mechanism which includes an actuating lever disposed adjacent the door for operable engagement therewith and whereby the trigger mechanism is operated to enable biasing apparatus to carry the signalstaff to the upright position as the door is opened.