if you still have the physical plate itself all you have to do is take it into the dmv and reregister it. unless its been unregistered for so long that someone else has gotten it.
the knukl has to do with the moose near it. http://i47.photobucket.com/albums/f193/crzyape177/MooseKnuckle.jpg see that for reference.
saw two good ones on the way back from savannah today. a University of Florida (Florida) Plate that read "GTFOF". even though I'm a UGA fan i still got a good laugh. (for those illiterate: "Get The Fuck Out of Florida") and a late 50's-early 60's yo woman driving a big Lexus SUV with a Georgia plate that read "BALDSAX"