Assuming, of course, you already have an engineered structure to install the banner on and you have secured the proper permits, you will likely want 18oz. reinforced vinyl material with webbing reinforced hems and internal ropes sewn into the top and bottom hems. You will want stainless hardware and thimbles at the attachment points, and stainless carabiners to install the banner onto the parallel wire rope fabricated suspension structure. Your permitting authority will likely require stamped drawings (I use Murdoch engineering).
Most any industrial banner manufacturer can make these (Tent and Awning companies can be a good local source). There are few companies that advertise this type of banner because most municipalities will not allow them. You might contact Material Promotions (888-757-8908), or any of a number of vendors that contribute to this website.
You will also likely be required to supply the municipality with an endorsed insurance rider naming the municipality as an additional insured on the certificate of insurance.
Good luck!