Is is legally binding since the 80s in Germany. Just mostly nobody bothers to protest a occasional error and it would mostly affect the teenager who delivers the ads anyway.
https://dejure.org/dienste/vernetzung/rechtsprechung?Gericht...
https://dejure.org/dienste/vernetzung/rechtsprechung?Gericht...
I also send nasty letters to parties who consider themselves exempt from that before elections (they're not).
If their job is to litter, then tough luck.