An identity disk is carried by few CovenantElites for security purposes. The identity disk is a small diskette that is meant to be read on a handheld reader. It contains information on its holder's name, rank, etc. It is similar to the concept of the Dog Tag used by the UNSC Marine Corps.
They are not often used, except when utmost formality is at hand, such as when an Elite wishes to meet with Prophets or other members of the High Council. In this case, they are also used in coordination with the DNA slot machines, to ensure the safety of the Prophets and Council members.