"F.U." stands for "Fairfield University".
But in Joe Lieberman's case, it might also be what he is saying to the handicapped by parking in a clearly marked handicapped parking space this morning.
Apparently Joe has caught a case of George Bush's "Above-the-law-itis".
Dear God, Senator, have you no shame? (photo from LamontBlog.)
UPDATE: Of course, those evil lefty photoshoppers are getting in on the act. Here's a photo on DailyKos's comments.