The United States Patent and Trademark Office will not protect your right to use your trademark against a third-party infringer, either in or out of court.  The obligation to protect what you have invested in your trademark resides with you.  This means that it is up to you, the trademark owner, to police any unauthorized use of your trademark.  But remember that your right to exclusively use your trademark is tied to the goods and/or services for which you received the trademark.

The legal rights that you received in your trademark because you registered your trademark with the United States Patent and Trademark Office are not permanent or indefinite.  Without you taking certain actions to maintain your trademark.  A Section 8 Declaration of Continued Use or Excusable Nonuse is due six years after your trademark registration date, or within the six month grace period thereafter.  A Sections 8 and 9 Combined Declaration of Continued Use and Application for Renewal is due 10 years after your trademark registration date, or within the six month grace period thereafter.  Your federal trademark will be cancelled or expire if you do not timely file.  If your federal registered trademark is cancelled or expires, the only remedy is to initiate a new federal trademark application process.  Depending on how you used your trademark and whether you appropriately policed infringing uses of your trademark, you may find that your rights in and to your trademark may no longer be what they were during your initial federal trademark application.