Perhaps the concern is not with Danica's use of sign language on the bus, but rather with the fact that her parents are suing the district over Danica's loss of hearing last November when a fellow student set off a bottle rocket near her head in a school hallway. We don't know whether the Leskos' lawsuit has merit. And, obviously, Danica is able to communicate through normal language skills learned before the November incident. But if the only way other students can communicate with Danica is through sign language, then she needs to know how to use it. If that means signing on the bus, so be it.
Signing involves no greater safety hazard than using the spoken voice.
Maybe it is the school administrators who should sit down and shut up.