Perhaps we could have some sort(s) of furnishing(s) that are Coliseum-related, so that we could show those off?
And they could be purchased with Krogmo coins!
Either we could donate those into the treasury like crowns, or there could be a quote/price for each furnishing (much like the fill bar in bribing King Krogmo) where individual knights could choose how many coins they'd like to submit towards a cause!

And perhaps some very special furnishings could require something like "Must have been top _insert_minigame_here_ guild at least once."