While searching hard copy or online BGN databases in order to establish geographics, many PCC catalogers have encountered headings prefixed with a plus sign (+)
Our ever-resourceful friends in CPSO have finally determined that names preceded by a "+" have been used in past NIMA products; however, no authoritative source is currently available for the name form. These names are considered "Not Verified" and are not normally used on current NIMA products or for official US Government purposes unless no other name form is available.
For more info, contact Cataloging Policy and Support Office at LC - cpso@loc.gov