I would have thought it was necessary to get permission to put banners up but I guess if you don't ask permission then you can't get a refusal
On the matter of musicians, when I was in the town on Saturday I saw a lone Piper all dressed up in traditional Scottish kilt etc playing away on his bagpipes and very well too. It was freezing cold but he played on and on. Passing by a couple of hours later he was still there and it was dark then. I put some money in his bagpipe case. Took a photo on my phone but it is a little dark. Perhaps someone will know who he is, maybe he could play on Market Day.
Keith, when I lived in Cheam Village many years ago now, I used to go to Abbey Mills all the time. As you say it is a great market place. I still have some objets d'art that I purchased there, the food stalls were awesome. We would sit by the mill eating our delicious lunch, sweet memories.