What identifier prints on the bag tag of selectee customers?

The identifier that prints on the bag tag of selectee customers is "ssss." This code is used within the context of airline security protocols, specifically those associated with the Transportation Security Administration (TSA). The "ssss" designation is an acronym representing "Secondary Security Screening Selection," indicating that a passenger has been chosen for additional security measures before boarding. This tag alerts airline personnel and security staff that the passenger may require further screening, which is a common practice in ensuring the safety and security of air travel.

The other options do not have any special significance related to security screening or passenger identification in the context of air travel. Therefore, "ssss" is the correct and relevant identifier for this situation.