There are two ways to tell if the timing belt has been replaced. One is obvious-you are looking at a service receipt showing the replacement.
Swimlane diagrams are used whenever you need to show activities, tasks, or process steps which are being performed by different actors/roles. You can use swimlanes to group activities in an activity diagram or process flow by any category what you need: by role, by system, by department, etc.
The purpose of the school bus sign and hazard warning lights is to make other road users aware that when the vehicle is stationary children are likely to be getting on or off the bus and may be crossing the road. Other road users should, therefore, be very cautious when passing a school bus in those circumstances.