Prohibits, Restrictions, Observations

http://pe.usps.gov/text/Imm/il_016.htm#ep1640129

Prohibitions (130)
Counterfeit postage stamps.
Documents, books, printed papers, engravings or other articles contrary to public security.
Firearms, sabres, and swords for military use.
Firing caps and loaded metal cartridges for portable firearms.
Machines and paper for making cigarettes.
Salt.
Textile fabrics.
Weights and measures.

Restrictions
Coins; paper currency; banknotes; currency notes; securities payable to bearer; jewelry; manufactured and unmanufactured platinum, gold, and silver; precious stones; and other valuable articles are admitted only if sent in registered First-Class Mail International shipments.
Monthly or weekly journals are admitted to the extent of three copies per person and per issue; they are subject to a permit from the government if they exceed the limit of three copies.
Tobacco and ginseng may only be imported by the Korean government.

Observations
Articles addressed for delivery in Korea should show the name of the addressee, street, district, town and province in Korea. The address should be shown also in Korean characters, if known.
Service is available only to the provinces comprising the Republic of Korea, i.e., provinces south of the 38th parallel of latitude.
The following is a list of the provinces comprising the Republic of Korea:
Cheju-do
Cholla-namdo
Cholla-pukto
Ch’ungch’ong-namdo
Ch’ungch’ong-pukto
*Kangwon-do
*Kyonggi-do
Kyongsang-namdo
Kyongsang-pukto
The provinces marked with the asterisk (*) are divided by the 38th parallel of latitude, and it is the responsibility of the mailers to determine that the post offices to which their parcels are addressed are located south of the 38th parallel. Mail addressed to offices north of the 38th parallel will not be forwarded to destination but will be treated as undeliverable.