The phrase "big banner" refers to a large, eye-catching sign or advertisement that is often used to promote or announce something important or significant. Full definition
Please, please, please, people show up with big banners at the emirates to get rid of wenger and kroenke... changes may still not happen but at least still do our bit... (justarsenal.com)
The Bole youth are walking through the town with big banners of #iChooseJM, distributing stickers proudly stating #iChooseJM and sharing fliers showing some of the achievements of President John Dramani Mahama. (ghanapoliticsonline.com)