Godot gives you a warning if you declare a signal, but don't use it in that class. In my case, I use it in another class, but it belongs to the class I declare it in because it is emitted there, just via some indirect data-driven stuff.
This is a surprisingly
tough case for Godot.
It's simply impossible to solve. There's no way to correlate a signal declaration to its emission in a completely different place (especially when not even in GDScript, such as an animation, or if it's emitted in some script made in another language). (Don't say "you could solve this with AI." You can't reliably, and it wouldn't be worth the cost even if it could.)
So, if you can't reliably detect if it's used, should they just eliminate the warning entirely? I don't know. Sometimes, signals are meant to be emitted straightfowardly, and there are dead signals lying around.