I hit the books and found this item in Geoffrey T. Carlton's excellent Star Wars Super Collector's Wish Book (fifth edition). It's labeled as being from the fan club, limited to 1,500 pieces. But when I'm researching an item, I really like to have a second opinion, so I headed for the computer.
I've scoured the web trying to find any more information about what this slightly-off looking piece is, but I've found next to nothing about it. I've used keywords like ceramic, vader, bust, fan club, etc... and still nothing. I've seen two of these busts in a bootleg/knockoff collection on the internet, so that makes me question whether this is a bootleg collectible or what.
This appears to have once been a blank canvas for craft lovers (or Star Wars fans who felt creative) to decorate. This one has a note left on the bottom. MERRY CHRISTMAS 1978 FROM MAX, DON, LISA, + LESLIE
This is one of those collectibles that I'd love someone to leave a comment about, explaining what it is and where it came from.
UPDATE: Someone left a comment telling what they think this is! Dan Elman wrote "I'm willing to bet that this example is a fan-produced knock off of the Darth Vader bust model kit made by MPC." and "What's happening there is the craft-wise ceramics artist copying other licensed collectibles of the day. I would not be surprised if they used the licensed collectible to make a rubber mold in order to copy the form. I'd bet anything your Darth is similarly copied off that MPC bust model kit." Thanks for the reply, Dan, it's much appreciated. The rest of you can read Dan's full comment in the comments section below.