IMHO, if one is pulled over for something, and doesn't tell the cop that they're carrying, if they have to get out of the car for something (i.e., inspect a damaged taillight, etc...), and they flash/print on the way out of the car, they're gonna get a piece screwed into their ear... Way I see it, it's (1) polite to let 'em know, and (2) a good way to let fence-sitting cops see how nice and polite we are...