ГОСТ 8591 - a standard from the time of the Soviet Union, of the National Standards Institute of the Soviet Union. This standard deals with Manholes for cable wells of telephone sewerage The number appearing after the standard indicates the year of the standard, for example 8591-57, year 1947.
An example of a cover that carries the standard on the "ultimate manhole covers" site. From this lid the picture that appears in the general section was taken.