At one point in time sigil hued leather/metal armors(and other items) were sought after and even deemed illegal to own. Over the years leather and metal dye tubs have been used through various npc sell/buy back exploits to obtain the sigil hue, thus allowing people to dye all sorts of items the sigil hue. Id say if the armor is not double exceptional and player crafted maybe fetch 100-200k.
Some sigil items that have retained value are ones that could not be replicated.. wooden items (non furniture), bone armor pieces etc.
Hope that helps..