Ribbons keep people from talking about a topic their giver chooses. If we ask them about that matter, they have to tell us their lips are sealed, and if they try to get around this or plain forget then the ribbon kills them. I dunno if it works that way for Bigsby, but it might and Zehn better be careful about what he says or we're out a cop.
Since the Woodsman is with us again unexplainably (I'm wary about how that happened as to my knowledge we don't have anybody with revivification powers, and I really don't like how he had a ribbon on him as soon as he woke up unless he was Vivian's first target)