retracing the validity of a key

[Christoph Groth]

Hello,

For some key in my keyring that GnuPG considers valid due to the web of
trust I would like to understand why it does so.  I can list all the
signatures with --list-sigs, but is there any way (short to writing a
script myself) to mark those signatures that are actually considered
trusted?

Thanks,
Christoph