When Cranmer is about to be carted off to the Tower, he busts out a very special ring. Check out what he says to the council members about it: "By virtue of that ring, I take my cause / out of the gripes of cruel men and give it / to a most noble judge, the King my master" (5.2.164-166).
You probably noticed how everyone is surprised by the ring, and they backtrack a little once they see it. That's because the king's ring was a symbol of his favor; he didn't go handing out rings to just anybody. Anyone wearing the king's ring is pretty much off-limits.
We say "pretty much" because as this play shows, the king's favor can change. The ring is supposed to be something permanent, but we've seen how things that are supposed to be permanent—like Henry's marriage to Katherine—can be cut short if the political reasons are good enough. Cranmer was lucky enough to keep Henry's support while Henry lived, but Queen Mary I—Katherine's daughter—found him guilty of treason and had him burnt to death in 1556 (source).