Abstract: The disclosed signal device has a base plate and a signal plate, each plate having a threaded member secured relative thereto. A helical coil spring is threaded onto the respective threaded members, to become fixed between said base and signal plates. The signal plate has adjacent an edge remote from the spring, a tab portion angled about an axis disposed transverse to the threaded member. A double sided adhesive tape, bonded on one side to the face of the base plate remote from said spring, has the other side on the base plate, but it is yet covered by a removable facing. After removing the tape facing, the base plate may be positioned with the adhesive side against the exterior wall structure of a roadside mailbox, at a suitable spacing from the adjacent open end and door of the mailbox.