Google stated displaying a bar in the Gmail just above the tools, which informs Gmail users that their messages are automatically forwarded to another email address. The messeage "you are forwarding your email to ..." would appear for about 3 minutes every time you open Gmail starting this week.
Google citing the reason for this message that some malicious software or other people who gain access to your account can setup auto-forwarding. "For about a week, this notice will appear for a few minutes each time you sign in to your account. Displaying the notification in this way helps ensure that you have a chance to see the notice, rather than someone who might try to gain unauthorized access to your account and use this setting improperly. The notice will disappear immediately if you choose to disable the forwarding setting, but that decision is up to you," mentions Google.
For some reasons, if you do not want to show the message, you can either temporarily disable auto-forwarding, or switch to the simplified HTML interface or pin the Gmail tab if you use Chrome, Firefox or Opera.