No one naturally pronounces anything as language is a purelly intellectual product.
In auto jargon though and some others, the abreviation MK followed by a roman numeral has been used (not only by Lincoln to signify a generation of a particular line). The first and second Continental were so commonly known as MkI and MkII that Iaccocca cleverly used Continental Mark III (using the full word) in the early 70, jumping like 3 generations od Continentals, to name Lincoln's newest coupe. Then that name went on until the sometime during the 7th generation when the Continantal name was dropped to be used exclusively by Lincolns midsize sedan.
Lincoln is just taking advantage of the enormous recognition and ties with its history that this words has. Do I think that they are doing it in a clever way? Sadly not. Although I don't think it will cause any damage I hate to see the Mark denomination so overused and I wonder what will they do if they ever decide to revive the coupé line as it is rumored.
Other cars are know by their generation designated by the abreviation MK pronounced Mark, most commonly known the VW Golf or Rabbit.