In 1796 optical telegraph stations were built at Grisslehamm and Eckerö and Signillskär. Abraham Niclas Edelcrantz designed the stations which used 10 shutters which could display over a 1000 different patterns. Although the system did not last long in the Swedish empire the same design was used elsewhere in Europe.
     The stamp shows the tower with the shutters at Signillskär, with a map of the Bay of Bothnia. A line shows the line of sight between the stations.