If a financial institution is not a member of a recognized Medallion Signature Guarantee Program, it would not be able to provide signature guarantees. Also, if you are not a customer of a participating financial institution, it is likely the financial institution will not guarantee your signature. TCF Bank offers a signature guarantee service if you need to guarantee the signature on a specific document is genuine. The service is free for existing TCF Checking, Savings, Certificate and Loan customers.