FJ actually means "Fake Jeep" when I speak about my coworker's FJ Cruiser

and there was no official "LJ" designation for the TJ Unlimited... that was started by the enthusiasts...

The JK is the first Wrangler "style" (open top) Jeep in which the 2-letter code didn't end in "J".. (reason I say "style" is because CJ's were NEVER called Wranglers, that name started with the YJ)

speaking of FJ... there really was a Jeep FJ... it was a compact fleet/delivery van made by Willys from 1961-65

 

I like to think it means "Just Kill"