The most obvious one is
His claws peep through like Rays of Light
It is kind of an odd comparison, but it is a comparison. His claws come out like rays of light means that the claws are barely noticeable as he unsheathes them. They are however like the first light of dawn or the last light of dusk. He's sort of checking them to make sure they are there.
The theme of revenge starts off very early in the play when Hamlet speaks with the ghost of his dead father and when the ghost tells Hamlet how Claudius murdered him which Hamlet was extremely angry and overtaken with feelings of responsibility to right the wrong that he been done to murder Claudius
A - Not a knocker but Marley's face
This shows that the knocker transformed to the supernatural by becoming not what it was - but the face of his dead co-worker.
