Pl3xMap-Banners is an addon to Pl3xMap that allows players to display their banners the same way you can see banners on the vanilla map. Players with the pl3xmap.banners.admin permission need to right-click with an open map in their main hand on a placed banner to make it visible. Left-clicking will make the banner disappear from the map.
Pl3xMap-Signs was used as a template for this addon.
Grab the working build from https://github.com/granny/Pl3xMap-Banners/releases/latest