Note that this lid has two manufacturers: PAm and WN which is the symbol of Wallner Neubert REXEL - The trademark name of a cover type in the manufacturer PAm
The lid is similar to other covers of the same model in other countries, for example Click for cover's details
GS - Spheroidal graphite cast iron - a special cast iron in which the crystallization of carbon has been slowed down, which makes it close to steel - also called ductile iron (Thanks to Vuori Susi for the clarification)
If you know the meaning of the following symbol Click for a larger image (which is likely to symbolize any standard) click on the question mark