must be adapted to the shelves on which the display is to be mounted in fig2 to which reference now is made the device of the invention is shown broadly as a generic block diagram in this diagram the display is shown again and due to the fact that the display has been located in a rectangle indicated by dot and dash lines 14 within which there is also a block 15 it has been indicated that the display and the block form together a unit which can be included entirely in the housing of the display the block 15 represents an electronic control unit which is connected to the display for the control thereof and this control unit is provided with the receiver 13 mentioned above signals are transmitted to the control circuit 15 via the receiver 13 from a circuit 16 for serial transmission via a transmitter 17 and a control device 18 is connected to the circuit 16 said device comprising principally a microcomputer and can be constructed as a portable unit a so called key the appearance of which resembles a minicomputer or a remote control for tv sets alternatively there can be connected to the circuit 16 a shop computer 19 which controls also existing cash registers the circuit 16 with the transmitter 17 preferably.