Several symbols are used to provide notice of intellectual property.
©
The copyright symbol, ©, indicates that the creator of an original work has the exclusive rights to publish, reproduce, or sell it. Books, music, scripts, artwork, photographs, and other works of authorship can be given copyright protection. The copyright symbol is usually followed by the year of first publication and the name of the copyright owner.
™
A trademark’s purpose is to uniquely identify a business as the source of a product or service. Trademarks apply to distinguishing features like names, phrases, or logos, but can be more broadly defined to include colors, three dimensional shapes, and sounds. A trademark is symbolized by a superscrpt ™ immediately after the mark.
SM
Companies that offer services, rather than products, can place the service mark symbol, SM, on their advertising.
®
Once an original work is created, it is implicitly granted copyright protection. In much the same way, a distinctive name or logo is automatically trademarked; no registration with state or federal agencies is required to apply these symbols. A registered trademark, indicated by the ® symbol, can only be used after registration with the U.S. Patent and Trademark Office. This symbol replaces the less formal ™ and SM. Federal trademark registration requires the periodic payment of fees, but offers greater legal protection in priority disputes.
WikiAnswers on C v. TM v. SM v. R
wiseGEEK on trademarks and registered trademarks