 In every New York visual effects scene with flying traffic there is  a flying bus with the Digital Domain (the facility responsible for  most of the VFX) internal reference, or shot name, stenciled on the  roof of a bus. The instructions for the visual effects team were to  include one bus with the shot name but then all other buses and  traffic could have personal references including birthdays,  initials, etc. The front marquee for a buss destination and side  billboards were customized by the artists at Digital Domain to  reference, invisibly or subliminally, some personal stamp or  message.