Maybe we have a different understanding of "signature", in my mind its the whole type, return (remember an override can be any covariant type, its not necessarily exactly the same as the `Iface::` declaration), qualifying scopes, name, and parameters, but IIUC you are using "signature" above just for the parameters?
Anyway, I would have to try and use it without the file and line and see if I can adapt to it, so I can have a better idea of whether the file really is useful or just a habit I have.
I mean, I'm not against having file:line, and @ntrel suggested having it as a tooltip IIRC, I'm just looking at ways to shorten the selection box since your image in the OP is indeed hard to use.