Abstract: A kit for adapting a conventional rural mailbox to one which provides a visual signal to advise any one interested that the mailbox has been opened. The kit includes a large signal indicator which is protected within a housing having a transparent portion, said housing being attachable to the rear of a conventional mailbox together with an additional indicator signal which is actuated simultaneously with said first indicator, said second signal being visible from all directions, and latch means for retaining both indicators in a position hidden from view, with additional trigger bar structure attachable to the hinged front door of the mailbox for actuation thereby when said door is opened and movable to release both indicators so that they may drop by force of gravity from their out-of-sight position to a position which is visible.