In the spirit of community and what I believe to be an untapped resource in the game world, why not make banners useful for more than just buffs? An entire window pops up when using them that give a generic “Please enjoy our compliments” message.
Why not make it something more in the spirit of opening out to your server, others, even? A message written by the guild who placed the banner would be a far better use of the window. Everyone just dismisses it in favour of simply obtaining the buff and going about their business. Maybe more “personalised” messages would stop people a little more often and tell them about the guilds who put them up for everyone? It would, I imagine, even be simple enough to implement. I imagine there’s other functions it could have too, with a little more time.