Below the city emblem appears the text: documenta-Stadt, indicating the Documenta exhibition of contemporary art, which takes place in the city once every 5 years. The exhibition, considered the most important in the world in its field, is so significant to the city that it appears on the city emblem.
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
The lid is similar to another manhole cover made by the same manufacturer