Can someone use your signature without you knowing for a co-signature?

Yes, someone can potentially use your signature without your knowledge for a co-signature, especially if they have access to your signed documents or personal information. This practice is considered forgery and is illegal. If you suspect that your signature has been misused, it's important to report it to the authorities and take steps to protect your identity. Always be cautious about sharing personal information and monitor your financial accounts for any unusual activity.