Arcane sigil, being an exclusive drop to Corporeal Beast, is used to create a Arcane spirit shield. Players can use this item on a Blessed spirit shield to create the 'Arcane spirit shield. However this process is irreversible, players decide to use this method of acquiring the Arcane shield.
Arcane sigil is a rare drop from Corporeal beast, leaving this rare drop extremely rare due to the numerous other rare drops this monster has. Players are forced to get this item from either getting it as an extremely rare drop, or to trade with other players. This can be avoided by visiting the Credit Shop to buy the end product Arcane spirit shield.