Abstract: A signal indicating device mounted on the wall of a cover box or the like. The box encloses electrical components such as contactors, relays and other devices for registration of e.g. the operational conditions of an industrial process. A printed circuit indicating or control card is connected between the electrical components and the signal indicating device. The signal indicating device comprises at least one row of signalling lamps mounted on a printed circuit card, which is hermetically enclosed in a case with the signalling lamps projecting through holes formed in one of the sides of the case. Also mounted on the printed-circuit card are plugs passing through one side of the case so as to project externally thereof and arranged to be connected with corresponding plugs on the printed circuit indicating or control card via an opening formed in the wall of the cover box.