This is not a substitute for legal advice.  An attorney must be consulted.

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A trademark is any word, symbol or device, or combination thereof, that is used to identify and distinguish a person's goods from goods manufactured or sold by others and to indicate the source of those goods, even if that source is unknown.  15 U.S.C. § 1127. A service mark is similar to a trademark, except it relates to services rather than goods.  Trademarks serve three main functions:  (1) distinguish goods from those of competitors; (2) guarantee quality of the goods; and (3) advertise, promote and sell the goods.  Traditionally, the legal protection of trademarks was considered part of the common law doctrine of unfair competition.  Today, both federal law and the state law of all fifty states provide registration and enforcement of trademark rights.

In order to be protected under trademark law, a trademark must be "distinctive."  This means that the trademark must distinguish the trademark user's goods from the goods of others.  Trademarks vary in distinctiveness, ranging from (strongest to weakest):  fanciful (Exxon), arbitrary (Apple computers), suggestive (Coppertone suntan oil), descriptive (Weight Watchers food products) and generic (linoleum).  Fanciful, arbitrary and suggestive marks are inherently distinctive, and they are registerable without further evidence of distinctiveness.  Descriptive marks, absent a showing of "secondary meaning," are not registerable as trademarks.  A mark acquires secondary meaning through exclusive use for an extensive time period such that the public associates the mark as an indication of origin, rather than in its primary descriptive sense.  Generic terms are not protectable at all. 

When properly used, a trademark is always an adjective and never a noun or verb.  Allowing a mark to be used as a noun may result in the mark becoming generic.  Examples of former trademarks that later became generic include aspirin, escalator, thermos and cellophane.  Trademark law requires that the mark cannot merely be used in advertisements and must be affixed to the goods or their containers or displays associated therewith or placed on the tags or labels attached to the goods or containers.  15 U.S.C. § 1127. 

Congressional power to regulate trademarks arises under the Commerce Clause of the Constitution (U.S. Const. art. I, § 8, cl. 3).  The federal trademark law, usually referred to as the Lanham Act (15 U.S.C § 1051 et seq.), provides for federal registration in the U.S. Patent and Trademark Office (PTO) of trademarks that have been used in commerce.  Federally registerable trademarks are registered on the Principal Register, while "marks capable of distinguishing applicant's goods or services and not registerable on the principal register" are registerable on the Supplemental Register.  15 U.S.C. § 1091.  The legally binding rules of practice in trademark cases, which must be followed by applicants in applying for a trademark and the PTO in examining applications, are provided at 37 C.F.R. § 2.1 et seq.