In the episode, "The Taming of the Shrew" (Season 3, Episode 3), at around 13 minutes, 50 seconds, when Helen and Brian go to the senior's meeting, Brian starts writing on a chalkboard in the front of the room. The question mark that he writes keeps disappearing and reappearing all throughout the scene, at least nine or ten times. You can also see the word "MOMMY" written on the upper-right part of the chalkboard with a heart around it, and then it disappears.