SV is probably an abbreviation for SPILDEVAND (wastewater).
The pentagon inside which the crown is located is the outline of the Kastellet fortress in which the lid is located. The crown is part of the fortress’ symbol.
The lid is similar to another manhole cover made by the same manufacturer
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.