Trademark

Trademark (symbolized by "^TM") is a word, phrase, symbol or design, or a combination of words, phrases, symbols or designs, used by a company to identify and distinguish the source of its goods from other company's goods.

It is not required to register a trademark with the U.S. Patent and Trademark Office (US PTO), but registration with the "Principal Register" does provide several advantages:

• constructive notice to the public of the claim of ownership of the mark;
• a legal presumption of the registrant's ownership of the mark and exclusive right to the use the mark nationwide in connection with the goods and/or services listed in the registration;
• the ability to file a lawsuit in federal court to enforce the mark;
• the use of the registration with the USPTO to register in foreign countries; and
• the ability to file registration with the U.S. Customs Service to prevent importation of infringing foreign goods.

One may use the federal registration symbol "®" only after the USPTO actually registers a mark, and not while an application is pending. Also, you may use the registration symbol with the mark only on or in connection with the goods and/or services listed in the federal trademark registration.

Sources

USPTO information
Trademark registration