A more thorough explanation:

A signature card is a document used by financial institutions to keep track of a customer's signature and other important information. This helps the institution monitor financial transactions by comparing the signature on the card with signatures on checks, withdrawal slips, and other documents.

For example, when you open a new bank account, you will be asked to fill out a signature card. This card will include your signature, as well as other identifying information such as your name, address, and social security number. The bank will keep this card on file and use it to verify your identity when you make transactions.

Another example is when you write a check. The bank will compare the signature on the check to the signature on your signature card to make sure it is really you who wrote the check.

Overall, a signature card is an important tool for financial institutions to prevent fraud and ensure the security of their customers' accounts.