In the movie 'Dirty Harry' what is the name on the yellow school bus which has been hijacked by the Scorpio killer?

Scorpio calls and informs the Mayor that he has just hijacked a Deichsel Charter Service school bus and kidnapped seven children and the bus driver - "I've got the kids. You start screwing around, the kids start dying." Holding the city hostage a second time, he orders the preparation of a jet plane from the Santa Rosa Airport with ransom demands of $200,000, and then alerts them to his terrorist plan.