I don't think you need any sort of permission. I went to the O2 arena in london a couple of months back for a festival called "country to country" basically a load of country music artists, big names in the country industry, we're all playing on the big stage but also smaller stages dotted around and I was helping my girlfriend give out/dump a load of flyers advertising her website and at no point did anyone try to stop us or anything. I ended up playing a little game trying to slide them into people's bags or pockets without them noticing. Most I got was 4 on the run without being noticed. Windscreens may be slightly easier unless you're playing in traffic.