Before scheduled bus service starting at 6:30 AM, buses with character names on the destination signs ran prior to an hour before park opening to bring guests to early park breakfasts. Occasionally they would add a stop at a nearby resort e.g. Magic Kingdom trips going to Grand Floridian or other nearby breakfast location upon request.
Character names were used then for any bus not on a regular guest route. For better or worse it avoided having buses running with "Out Of Service" as a destination and guests inside visible through the windows.