Modern Warfare 2 was going to be called just that; taking a break from the usual Call of Duty tag. Why Infinity Ward decided to do this is beyond me, but it seems that taking away the Call of Duty tag lowered awareness in the game. However, Activision recently placed the CoD tag back onto the game in hopes of raising awareness. And it seems to have done as planned.
Nielsen’s Video Game Tracking service has followed awareness of the title through both name iterations and conclusively shows that the Call of Duty tag makes the consume more aware of the product. Personally, the fact that it is called Modern Warfare 2 sort of gives away the fact it has some relation to Call of Duty: Modern Warfare, but it seems people need a bit of handholding to understand when a game is part of a franchise. The full report can be seen here.