The US Coast Guard has released Policy Letter No. 02-04 which establishes the agency's policy on enforcement of STCW 95 during inspections of foreign-flag vessels during Port State Control (PSC) examinations. The certificates of officers serving on ships flagged by a state other than the one that issued their license must carry an endorsement from the flag Administration of the ship.
Seafarers (other than radio officers or radio operators) may serve in a licensed capacity for a period of three months if they have a properly issued STCW 95 license and satisfactory proof that an application has been submitted to the flag state for an endorsement. The Policy Letter also gives instructions on how to address and evaluate the crew's competence onboard ships whose Flag Administration is not a signatory to STCW 95.
Source: INTERTANKO