C/S означает Cargo Selectivity
http://www.tradegoods.com/helper/07abbreviation/abbreviation...

Подробнее:
The Cargo Selectivity System, a part of Customs' Automated Commercial
System, specifies the type of examination (intensive or general) to be
conducted for imported merchandise. The type of examination is based on
database selectivity criteria such as assessments of risk by filer,
consignee, tariff number, country of origin, and manufacturer/shipper. A
first time consignee is always selected for an intensive examination. An
alert is also generated in cargo selectivity the first time a consignee
files an entry in a port with a particular tariff number, country of
origin, or manufacturer/shipper.
http://dictionary.babylon.com/cargo_selectivity_system/

а также:

http://www.aseankorea.org/files/upload/board/66/6/part1.pdf