Actually, it just has a name "Aegis of the Zuma". That no more makes it property of the Zuma than the name "Shield of Libiddo" means that the Shield belongs to Libiddo. Or that Ucdauh's Spear belongs to someone named Ucdauh? (sp?)
How is Brom to know that the Zuma stake a claim to every item that bears the name "of the Zuma"? If Brance got his hands on one of those, he would not instantly assume that the Zuma own it, and that he should give it back to them. If the Zuma want to claim that is the case, then the Zuma need to make that info public. Which, so far as I know, they have not.
All true. Though, Brom definitely does know that the Zuma are seeking the items. Several people do. Brom knows because he—according to Garret (I know, right)—was offering to collect them in exchange for salvation. Really, anyone who interacted with Garret would probably have learned that the Zuma were desperately seeking their preciouses.
