A bank guarantee is a promise from a lending institution that ensures the bank will step up if a debtor can't cover a debt. A medallion signature guarantee must be completed in person because it confirms your identity, signature and legal authority to transfer securities.A letter of instruction is a document that guides a designated individual or entity on how to carry out specific actions or wishes after the author's demise. The Letter of Instruction must be signed in the presence of the individual guaranteeing your signature. How to fill out the Bank Letter of Guarantee Template? Bank of America provides notary services free of charge in all financial centers. Schedule an appointment and learn what is needed for a notarization. This letter requests the issuance of a bank guarantee from ICICI Bank. Date: TO: Silver Auctions Arizona. You may obtain a Medallion Signature Guarantee stamp from a participating bank or brokerage firm where you hold an account. 2.