A trademark (identified with a "TM") can be many things. It may be a word, phrase, symbol or a design, but it can also be a combination of words, phrases, symbols or designs. The common link is that a trademark is used to identify a specific item, product or brand. A service mark ("SM") is very much like a trademark except that it identifies or distinguishes the source of a service rather than a product. Normally, a mark for goods appears on the product or on its packaging. In most cases, a service mark appears in advertising for the services.
A trademark is not a copyright nor is it a patent. A copyright protects an original artistic or literary work. An invention is protected by a patent. (For more information about patents, try the patent section of the US Patent and Trademark Office or contact the Patent Assistance Center at (800) 786-9199. For copyright information, check with the Library of Congress.)
Copyrights and patents eventually run out, but trademark rights can last forever if the owner continues to use the trademark to identify goods or services. Federal trademark registration lasts 10 years, but the registration can be renewed every 10 years. There is quirk in this process, so be careful to note that between the fifth and sixth year after initial registration, the trademark holder must file an affidavit with certain information about usage to keep the registration alive. If that affidavit is not filed, the registration is canceled.
Registration of a trademark is not required, but it does provide several advantages. Benefits include formal communication to the public about your ownership and right to use the mark for the purposes explained in the registration. If there is a legal question about use or ownership of a trademark or service mark, registration carries a lot of weight and can head off infringement law suits.
There are no federal laws regarding the use of the designations "TM" or "SM" with trademarks. There may be local and or state laws (plus overseas regulations) regarding these symbols. The right to use the ® symbol, however, requires the federal stamp of approval.