it's called PREM and it pertains to worthless securities
"Once six years have passed and the positions have been moved to DTC via its “position removal” or PREM function, the security is automatically placed on a list of issues that are eligible for destruction. This list is then distributed via an Important Notice to DTC participants, who have three months to review and determine if there is any reason for not destroying the listed certificates".
"It also allows firms to remove the position from their books and records as well as eliminate the security from the statements they send to their customers".