double d
A) The infamous logo of the kids' TV show Double Dare, in which the first letters of the words "Double" and "Dare" are linked together. Also called the "Dueling D's" when early cartoons showed the animated letters throwing pies and spraying seltzer at each other.

B) The large, white circle in the center of the "Double Dare" stage floor, which featured the above-mentioned logo printed in the middle. Often used as a marker during the show's physical challenges.
A) "What color were the Double D's in the 1989 season?"

B) "You can go anywhere on the stage that you want as long as your toes don't touch the Double D's."