Final answer:
Orange flags on double deck buses usually signal that the bus is at full capacity or out of service. These visual signals are part of public transportation's communication methods and can vary culturally.
Step-by-step explanation:
The orange flags that are sometimes held out at the back of the double deck buses serve as a visual signal. They are typically used to indicate that the bus is at full capacity and cannot accommodate more passengers or, in some cases, it may signal that the bus is out of service. This use of visual signals is important in public transportation systems around the world and varies from one place to another. For example, in some cultures, specific gestures or signs are used to hail a bus or communicate with the driver about stopping, as seen in practices from Cairo, Egypt to Dublin, Ireland.