"Next to the conveyor belt a man is busy reading his newspaper, the front page showing an advertisement of car brand Mercedes, which had begun to sell cars in Eastern Germany no sooner than after the reunification".
This is a poor sentence, not only because of the incorrect use of "advertisement of".
"The advertisement of controversial products such as cigarettes and condoms are subject to government regulation in many countries."
This is fine. As in Raymott's example, it refers to the act of advertising.