There are two types of trademark protection: State and Federal. State trademark protection is typically through common law, but many states do have statutes and a registration process. Federal trademark protection is through the Lanham Act in Title 15 of the U.S. Code. Tautologically speaking, state trademark rights only extend to that state's border, whereas federal rights cover the entire United States.
If an entity does not have a mark registered with the United States Patent and Trademark Office ("USPTO") or in the state or states where they do business, there still are remedies likely to be available. Unfair competition laws will be available in any state, and suit can be brought in federal court under the Lanham Act under the provision for "False Designation of Origin." Remedies for violations of state common law trademark rights may also be available.
There are five types of marks: Generic, Descriptive, Suggestive, Arbitrary and Fanciful. "Generic" marks refer to a set of which a particular product is a subset. For example, "Beer" as a trademark for the alcoholic beverage beer would be generic. "Computer" for computers would also be generic. Generic marks are never registrable with the USPTO, and they should never be protected in any state.
"Descriptive" marks are those that describe a quality or characteristic of the goods. Descriptive marks are protectable only when they have attained "secondary meaning." "Secondary meaning" means that there is an association in consumers' minds between a mark and product. If a descriptive mark does not have secondary meaning, it is not protectable. "Suggestive" marks require a degree of imagination in order to determine the product to which a mark refers. There is no description of the product in the trademark, only a suggestion of it. Suggestive marks are inherently distinctive, and protectable without evidence of secondary meaning.
"Arbitrary" marks use common words in new and unique ways. The best example of an arbitrary mark is "Apple" for electronic devices. Arbitrary marks are inherently distinctive and protectable without secondary meaning. "Fanciful" marks are words invented for use as a trademark. They are inherently distinctive and protectable without secondary meaning.
Basically, the more creative a trade name is, the more easily protected or protectable it is as a trademark. If a businessperson or entity comes up with a trade name and it is easy to determine the field or industry in which the business competes, it is probably not a good trademark. If you are a person or business that already has come up with a trade name that happens to be descriptive, you can still have a protectable mark if you can prove that the mark has gained secondary meaning. If you have a generic trade name, it cannot be protected as a trademark.