What must customers inform banks about to protect against fraud?

To effectively protect against fraud, it is crucial for customers to inform their banks about any forgeries. This is particularly important because forgeries can lead to unauthorized transactions and potential financial losses. By promptly reporting any suspected forgeries, customers enable their banks to take swift action, such as freezing accounts, investigating the transactions in question, and preventing further unauthorized access.

Keeping the bank informed helps to safeguard accounts and maintain the integrity of financial transactions, which is vital in today's digital banking environment where fraudulent activities can occur rapidly. The other options, while they may be important for other reasons, do not directly relate to the immediate prevention of fraud in the context of bank transactions.