Go North East Streetlites need engine off but ignition on to adjust steering column (I'm sure Streetdecks are the same).

Arriva Streetlites, have a 'secret button' which sounds the horn to start the engine.

Some of GNEs ex Manchester buses have similar features (as did the second hand Citaros).

Another safety feature found on E400's (definitely the Arriva ones when I was there), when you engage reverse there is a yellow button that needs pressing or reverse won't engage. I believe older Tridents also had a similar feature.