The United States Patent Office defines a trademark as:
...a word, phrase, symbol, design or a combination of words, phrases, symbols or designs that identifies and distinguishes the source of goods of one party from those of another.
A service mark is essentially the same but it is applied to a service rather than a product.
Trademarks/service marks do not have to be registered with a state or federal government to be valid, but they must be actively in use. The rules, governing a mark and its use in other countries varies. Some countries require a mark to be registered to be valid. A US trademark does not necessarily confer protection elsewhere in the world. Where a trademark/service mark is registered depends on where the goods and/or services are being marketed.
In the U.S. TM or SM indicates that a mark is being used by a company but is not registered, only when a ® appears has a mark been registered with the federal government. Unlike a patent or a copyright, a federally-registered trademark/service mark can last indefinitely if the owner continues to use the mark on or in connection with the goods and/or services in the registration and files all necessary documentation with the USPTO, etc. at the appropriate times. A trademark or service mark can be registered at both a state and a federal level.
Trade Dress refers to “a product's physical appearance, including its size, shape, color, design, and texture. … trade dress may also refer to the manner in which a product is packaged, wrapped, labeled, presented, promoted, or advertised, including the use of distinctive graphics, configurations, and marketing strategies.” Basically how a product is packaged. It does not need to be registered to have legal standing, as long as the packaging is distinctive enough. In some countries it is included as part of the trademark itself, in others it is separate. Trade Dress is increasingly coming into play with the advent of the Internet and webpage design.
Researching a mark
US Trademark Searching (Select Trademark Search from the left hand column and follow directions thereafter)
Trademark/Service Mark Searching (Ohio) Can search by mark number, description or application name.
Trademark/Service Mark Searching (Other States) Contact each state. Some states have online databases available for searching, otherwise check with the state agency who handles trademarks, etc. about search options.
European Community CTM-Online
Registering a mark
Federal (Select the appropriate form, etc.)
Ohio (Select the appropriate form)
Other States (Select a state link)
European Community Trade Mark (CTM)
Guide to Registering Your Trademark or Service Mark in Ohio. (Ohio Secretary of State. Business Services Division)
Protecting Your Trademark: Federal Registration Rights and Responsibilities. (U.S. Patent and Trademark Office)
Service Mark (Encyclopedia). (The Free Dictionary by Farlex)
Service Mark (Legal Dictionary). (The Free Dictionary by Farlex)
Trade Dress. (The Free Dictionary by Farlex)
Trade Dress -- The Forgotten Trademark Right. (FindLaw. Robert B. Golden)
Trademark. (Citizen Media Law Project)
Trademarks: A Guide to Resources for Trademark Searching. (Public Library of Cincinnati and Hamilton County)
Trademarks Basics Fact Sheets. (INTA - International Trademark Association)
What is Trade Dress? (NOLO)