3 flyposters from same flyposter producers

The good news - you finally removed the mass of flyposters at George's Cross. Thanks. However, this mob have put up three posters up not far from the cross advertising their 'services'. So now we have the producers of flyposters flyposting. And they are not alone in that regard. Why can't the council enforce strict liability for such producers of commercial advertising material? Pass a by-law that forces printers to include an identifying PR code on what they produce. They know that these are illegally used, they even break the law themselves.