It shows to which expansion pack the items belong as an overlay in the Guild Bank, the Reagents Bank, the Inventory Bags and the Character Bank.
Have you ever wanted to sort your guild's bank and ended up abandoning the task because you didn't know exactly to which Expansion Pack each item belongs.
There are many addons that shows this information in the item's tooltip, but isn't it more comfortable to see it on the item itself, and not having to go positioning the cursor over each one.
If you are like me who likes to organize the content of the tabs by expansion/profession, this is the addon you were looking for and never dared to ask ;-)
Good luck or Justice!