The first thing you should do if you think someone is using your trademarked name is to get an intellectual property attorney and file an injunction, a court order to stop the use of your name while the legal process goes on. To successfully sue someone for infringing on your trademark, you’ll need to be able to show that you own a valid trademark, that it has priority (was registered first, for example), and that the defendant’s mark will likely cause consumers to be confused about which is which.