What identification must be affixed to a person entering a PL-1 or PL-2 area?

The identification that must be affixed to a person entering a PL-1 or PL-2 area is specifically an "Affixed E." This identification system is part of the security measures designed to control access to areas that require high levels of security (Pl-1 and Pl-2 areas). The "Affixed E" signifies that a person has gone through the necessary vetting and clearance processes to be granted access to these sensitive locations. It communicates not only the individual's authorization but also alerts security personnel to the specific level of access that individual has.

In contrast, options like a valid military ID or registration documents might serve as forms of identification but do not meet the specific requirements for access to PL-1 or PL-2 areas. A clearance badge likewise might imply authorization but is not the definitive identification that must be affixed, which is crucial for the robust security protocols governing these sensitive areas. Therefore, the correct identifying measure is the "Affixed E," as it is the required standard for personnel entering these secure environments.