Since this old thread is re-opened for additional discussion, allow me to revisit the original question: "Is it a violation if the 'Notice of Special Flood Hazards...' is not signed by the borrower?"
For a general audience, the correct answer is "it depends", not "yes." Nothing in the flood regulations requires a lender to obtain the borrower's signature on this notice form. The requirement (from Fed Reg. H) is:
(3) Record of receipt. The member bank shall retain a record of the receipt of the notices by the borrower and the servicer for the period of time the bank owns the loan.
Although receipt language and a signature line on the NSFH form may be the most efficient and popular way to create the record necessary to comply with this requirement, any other reliable method will be equally compliant. If your bank has a procedure that requires the use of forms with onboard receipts, then it's accurate to find a procedural violation when these forms are not signed--but you could still be in compliance with the regulation if the lender obtained some other type of signed receipt.
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...gone fishing.