So until now the idea seems to be OK for most of you...

Before doing that we should make a list of the Mk style of each make/model.
Remember that we can adapt it for a precise model.
And also that this is for the "unofficial" "Mk" number. Some of the following list may have the "mk"/"mark" in their real commercial name, so they are not concerned (I think about Jaguar and Lincoln for example).

Renault: A simple number? Or roman number?
VW: Simple number
Ford: "Mk." + roman number ? or normal number ? or it depends on the models ?
Triumph Spitfire: "Mk" + number, or roman if > 3
other Triumph: various styles currently... which one is correct?
Honda: hidden in model name, displayed like an extra info with number + "series" ?
Jaguar XJ: for the moment we use the Chassis code, I think it is better
Jaguar E-Type: "Series" + roman number ?
other Jaguar & Bentley: "Mk." + roman number, but then we do not have any model name
Opel: Letter (A, B, C, ...)
Lincoln Continantal: really part of the commercial model name, or simply "Mark" + number ?
Austin & Austin Healey: "Mk." + roman
Rover: "Mk" + roman
Vauxhall & Austin Healey: "Mk." + roman

By default and for those with only few models concerned... "Mk." + roman ?

List of "Mk": http://www.imcdb.org/search.php?resultsStyle=asList&makeMatch=2&make=&modelMatch=- 0&model=mk&modelInclModel=on&modelInclExtra=on
List of "Mark": http://www.imcdb.org/search.php?resultsStyle=asList&makeMatch=2&make=&modelMatch=- 0&model=mark&modelInclModel=on&modelInclExtra=on