Coupe. Then I explain its got a 4.2 V8 engine with a F1 gearbox, otherwise known as a Cambiocorsa. They then tell me that it has the boomerang lights, to which encourages the conversation further.
I don't think it was ever marketed as the "4200", but simply Maserati Spyder or Maserati Coupe, then either GT or Cambiocorsa depending on gearbox.
So, "Maserati Coupe Cambiocorsa" in my case if anyone asks!
I remember a similar discussion on the Ducati list about their model numbers. Churchill was right when he said two nations divided by a common language. Both sides of the pond were surprised when they learnt one side says "nine one six" and the other "nine hundred and sixteen".