GJS-500-7 also called GGG50 marks a strong and heat-resistant type of metal while GJS is a sign for Continuously Cast Spheroidal Graphite Iron - which describes a process in which the metal is continuously fed.
The lid is similar to another lid, and may be made by the same manufacturer
If you know what the symbol on the right side of the lid is, click on the question mark (The symbol is also found on other manhole covers, for example