This is more than a little off my usual path, so research was called for. I found great info at this site:
http://militaryantiquesmuseum.com/military_antiques.php
Banners - nobori - have a history of use in war and ceremony. This website calls them "going off to war" banners: "These commercially produced colorful banners were pre-printed with military designs. The family and friends would then personalize them with patriotic slogans and/or the soldiers/sailors name."