The Medani bell I’m aware of is the Blasting Chime. The basic concept is that the bell is used to warn people of danger, whether it’s a hand bell or a massive bell for warning a town. This ties to the broad idea of the Warden protecting their charges by warning them of threats. Of course, the point of the Blasting Chime is that in addition to warning, it allows the user to BLAST ENEMIES WITH SONIC ENERGY. This is an item from Magic of Eberron, which I wasn’t involved in, and it seems pretty bizarre to me; it’s unclear how amplifying the power of the Mark of Detection produces deadly force. However, I’d call this out as a concrete example of cooperation within the Twelve; Cannith can certainly create a thunder blaster, and they made this one to integrate with the Mark of Detection.

Beyond that and more generally, though, part of the idea of focus items is that they often work through sympathetic principles. The Mark of Detection is easier to channel when using a tool innately associated with warning or with perception; it’s easier to make a magnifying glass that enhances Detect Magic when you look through it than to make a sword that does the same thing. So the idea of a bell as a focus for an effect that warns or protects—I’m going to ring the bell and as I do, it allows me to See Invisibility—makes sense to me.