You can register a trademark using an online legal document preparation service; the fee depends on the application type. Once your trademark is approved and registered, you may legally use the registered trademark symbol -- an encircled letter 'R' -- when you use your trademark. The symbol informs everyone who looks at your trademark of its registration. You can sue another party who is using your mark without your consent, no matter what state the infringement occurs in.
Trademark registration isn't necessary for legal protection against unauthorized use. If you create and use an original mark, it becomes a form of intellectual property: a distinct creation of your mind. If you want to protect your trademark but don't want to register, you may use the unregistered trademark symbol -- the letters 'TM'. Using the unregistered trademark symbol indicates you haven't registered the mark but are giving notice of your rights.
Although you don't need to register a trademark, doing so gives you an immediate legal right to defend against misuse. For example, an owner of a registered trademark can ask U.S. Customs and Border Protection to prevent the import of products using a registered trademark without permission, but the owner of an unregistered mark can't. You have a higher burden of proof if you have to take an unregistered trademark infringer to court; you must prove to the court the mark is unique, your creation and being used in a way that violates trademark law. A registered trademark owner doesn't have to prove the mark is unique or his. You will have difficultly enforcing your rights in a state you're not using the trademark in. Registration is recognized nationwide, but an unregistered mark is usually only recognized in the area you're using it in. If you've created a trademark but haven't registered it or displayed it to the public yet, you can't stop another party from using it. An unregistered trademark is eligible for protection only when it's being used in connection with sales to the public.
Even if you're not registering your mark, you still need to check the database of trademarks registered with the USPTO to make sure your mark isn't the same as or very close to an already registered mark. The online preparation service you use likely provides a trademark search for this purpose. If your unregistered mark is the same as or close to a registered mark, the registered mark's owner may sue you for infringement if you use it. If you register your mark but don't use the registered trademark symbol or identify the registration, an infringer may use that fact as part of his defense. If an infringer uses a registered trademark but claims he didn't know the mark was registered because you didn't identify the registration, it may affect any damages you receive in court.