However, you are forbidden to touch them. Trademarks, intellectual property rights and copyright law mean advertisers can say what they like wherever they like with total impunity.
Screw that. Any advert in public space that gives you no choice whether you see it or not is yours. It’s yours to take, re-arrange and re-use. You can do whatever you like with it. Asking for permission is like asking to keep a rock someone just threw at your head.