Armor stand

From DwarfFortressWiki

An armor stand is used to hang armor on. Dwarves will currently hang pieces of armor that they acquire on armor stands in their rooms but won't use them. It can be made of stone, glass, wood, or metal.

As with the weapon rack, they may be used for laying down an official barracks. Outside of that, if you already have an armor stockpile, they will be largely for decoration and to appease nobles.