Does anyone know what the Blue Building in Centropolis is? And if you do you probably also know why when I updated my forum signature nothing happened?

Once you complete all the steps to enter the building, you'll have access to a few things that only the blue building has, like special quests which give you points you can spend to buy exclusive items from the blue building shop. It's also the only place where you can create the Bumbus pet species.

Forum signatures may take some time to update, so just wait a bit, and see if it changes.

quite often you can get items from the Blue Building cheaper by buying them from other users instead of questing there. If you don't want a Bumbus or the Achievements relating to the Blue Building, you can ignore it IMO.

The market for just about everything in Subeta changes over time Just because one item has dropped a lot doesn't mean that the rest of the economy has. TPTB at Subeta have been engaging in inflationary policy for two years now.