A bank letter is an official document from your bank that provides important information about your business' official bank account. Table 2 – Reserve Bank and Serial Number Relationship.Reserve Bank. Letter. Designation. Number. Designation. Did you receive a letter from the Illinois Department Of Revenue asking you to verify your identity? Bank or financial statement dated within past 6 months showing your name, date, the current balance, and type of currency. Go to "Finance" and click "Change Direct Deposit Info. " Fill in your bank details and upload a voided check or bank letter. No one has lost funds in an FDIC insured account! Set up Direct Deposit for a faster, easier, and safer way to get your paycheck or monthly benefit check. Do it in 3 easy steps!