Something like:

!TagSignedBy CAFEC00C1E

or maybe it should be a list:

!TagSignedByAnyOf
- CAFEC00C1E

Maybe the list should be in a file in the repo in the default branch?

!TagSignedByKeyIn .radicle/signers.json

Or something. Could piggy back on delegates, maybe.

In any case, the need is to be able to filter on tags signed by known, trusted signners.