When you open a joint checking account, you're responsible for any overdrafts and fees charged to the account, even if another person writes the bad checks. The bank holds every co-owner of the account responsible until any negative balance is covered. The major exception to this rule is when you're only an authorized secondary signer on an account and your name doesn't appear as an account holder.

Secondary Signers

Most banks allow you to authorize other people to write checks on your account, even if the person's name doesn't appear on the checks. This system is used primarily by businesses to allow employees to write company checks, but it also can be used with personal checking accounts. If you're an authorized signer on a checking account, but your name doesn't appear as an account holder, you can't be held responsible in most cases if a check bounces or you overdraw the account. The difference between a joint owner and an authorized signer can vary from bank to bank, so check with your institution to be sure.