FOUND: Keys near Kelvidge Mall, one of them is... concerning (Kelvidge)

Found a set of keys in the Kelvidge Mall parking structure, level 3 near the south stairwell. Ring has a house key, a car key (looks like a Vorran), a small brass one that's probably a mailbox, and one I genuinely cannot describe. It's not metal. It's warm. I put them in a ziplock in my glove box and the bag fogged up. If these are yours, tell me which level and I'll know they're really you. And maybe tell me what that fourth key goes to, because I've been thinking about it more than I should.