A trademark is a word, phrase, symbol or design, or a combination of words, phrases, symbols or designs, that identifies and distinguishes the source of the goods of one party from those of others. A service mark is similar to a trademark, except that it identifies and distinguishes the source of a service rather than a product. The term “mark” generally refers to both trademarks and service marks.
A trademark can be registered with individual states, or with the federal U.S. Government. A trademark can only be granted a federal registration if the mark is being used in interstate commerce. In other words, if the mark is being used exclusively in one state and there are no out-of-state customers, then federal protection is probably not available.
However, federal protection becomes available as soon as the trademark is used in interstate commerce, and the legal threshold for achieving “interstate commerce” is quite low.
Common law rights are legal rights in a trademark that one acquires just by using the trademark in commerce. The trademark must be distinctive (either inherently or having acquired the distinctiveness) and it must be in actual use in commerce. The goods or services in connection with the trademark must actually be sold. Also, you only have common law rights in the geographic area where you actually sell the goods or provide the services.