This field is set to No if the user is the first notification recipient. It is set to Yes if the user receives the notification as a non-replacing delegate (All or Cascade options), and if, at the same time, said user has the signature authority (if they do not have the signature authority, the notification does not appear in the workbench).
It should be noted that if this field is set to Yes, there is at least another line bearing the same sequence number with the No value in the table that stores the workbench data (there may be other lines with the same sequence number and the flag being set to Yes if there are several delegates with signature authority). The first signature on one of the concerned lines automatically updates all those lines that bear the same sequence number by considering them signed.