I've seen pics of those billboards online before. I'm going to side with the theory that they were commissioned by a group of local dealers. I'd say they were trying to attract people with champagne taste on a beer budget by pointing out that the Fury looks a lot like a Lincoln Continental, at least in side profile, but much cheaper.
They didn't capitalize the C in continental on purpose... Lincoln's lawyers would have been all over them to change it. As is, they could argue that they weren't referring to the Lincoln Continental but cars from continental Europe. After all, that was the inspiration for the naming of the Lincoln Continental.
All just conjecture of course.