From Fallen London Wiki (Staging)

When owned. The game can't check what you have equipped as a requirement, only qualities and items directly. That's why, when they want to tie something to equipment status, it will give a unique quality, which then can be checked. E.g. <a href="/wiki/A_Member_of_the_Crew_of_the_St_Elmo" title="A Member of the Crew of the St Elmo">A Member of the Crew of the St Elmo</a> affiliation gives the <a href="/wiki/Noticed_by_the_Merry_Captain" title="Noticed by the Merry Captain">Noticed by the Merry Captain</a> quality when worn which unlocks a card, making sure it'll only appear when you have really have the item on.