oz mark you're correct with your explanation of what the leters CIP stand for, but they are commercially sensitive people. For example, travel writers, management in travel agencies, managing directors, CEO's, CFO's and the like for medium to large businesses are generally given CIP status and it is printed on their boarding passes. Like Gold and Platinum FF's, it is something that the flight crew look out for when scanning the boarding passes as you enter the plane and ensure those designted with CIP are looked after.
By spending more time in the air than on the ground. "CIP" is always noted on my International boarding passes, not on purely domestic trips. I've never noticed it on a domestic boarding pass not connected with an international itinerary.