Q: How should the TIN type field be completed?
A: For item 16 – TIN type:
Identify the type of TIN recorded in Item 15. Select option “EIN” if the person has a U.S. Employer Identification Number (EIN). Select option “SSN-ITIN” if the person has a U.S. Social Security Number (SSN) or Individual Taxpayer Identification Number (ITIN). Select option “Foreign” if the person has a foreign TIN of any type. Box 4b also must be checked if the foreign person is an entity. Enter the person’s TIN type if known even if the actual TIN is unknown and Item 15a is checked. If a 9-digit TIN is entered in Item 15 but the TIN type is unknown, select “EIN” if the person is an entity and “SSN-ITIN” if the person is an individual. TINs that are not 9 digits are presumed to be foreign, so option “Foreign” would be selected.
This is addressed in the "FinCEN Currency Transaction Report Electronic Filing Requirements" guide, Attachment C.