How is a customer call from their seat indicated?

When a customer call is initiated from their seat, it is indicated by a blue light and a single chime over the public address (PA) system. This signaling system is designed to clearly alert the flight attendants that a passenger needs assistance, ensuring a prompt and efficient response.

The use of a blue light specifically differentiates it from other notifications within the cabin, allowing crew members to easily identify that it is a call from a customer. The single chime serves as an audio cue that complements the visual indicator. This combination helps maintain clarity and reduces confusion during flight operations, as it is crucial for flight attendants to quickly discern customer needs.

In contrast, the other options represent different forms of alerts or notifications that may not pertain specifically to customer calls from their seats, thus not fulfilling the specific requirement of indicating a passenger's request for assistance.