Having gained her attention enough that she wouldn't dismiss them as just being crazy, Jacen let Cathy do what she needed to do, demonstrate the proof that she knew them. He remembered the day in the video well, carving pumpkins with Allana, and just about everyone else in the city. It had been a good day and one he hoped Clary would eventually remember.
Gently, he lowered the cars back down again with the Force, not even damaging them a little as they landed. No need to anger innocent car owners after all.
He had no idea what sort of impact the video or the drawing would have, but he did feel a flare of hope when Clary asked who she was. She may have asked Cathy, but he answered quietly anyway. "You're a friend," he half shrugged. "So we're here to protect you."