No, not a cm shuttle. Pluto is the only cm parking lot with a character name.
It just means the bus does not have a destination in the computer It could be a bus on the way to the fueling facility, or on the way to being parked for the night, or on a special run assigned off line. It's possible it could also be a training bus, but they're supposed to use Training or Earning My Ears on the marquee.
The character name changes from time to time as the software is updated. There's only one character name in use at a time, except for buses that have missed a software update.