Q: How should the "RSSD Number" field be completed?
A: For item 66, RSSD number (of the branch) –
Enter the RSSD (Research Statistics Supervision Discount) number of the branch, if known. If multiple branches are involved in the suspicious activity, complete Item 66 for each branch for which the RSSD number is known.
This is addressed in the "FinCEN Suspicious Activity Report Electronic Filing Requirements" guide, Attachment C.