If you are a businessperson and are confident that you have an inherently distinctive trade name, or have a descriptive trade name but can prove that it has attained secondary meaning, it is imperative that you verify no one else has already registered the mark in the same class with the USPTO. The Trademark Electronic Search System, or TESS, is the starting point for this inquiry. The "Basic Word Mark Search" is the search that all first-time users should utilize. Upon entering the search term in the parameters, there may be several entries indicating that the mark is registered. If you click on an entry, it will show the mark and particulars such as the attorney of record, the class of the mark, and the mark's limitations.
If two or more entities have the same mark, it does not mean that there was a mistake. It does not mean that the USPTO erred in issuing multiple registrations on the same mark. It simply means that the marks are in different classes. For example, "Delta" is a registered mark for a faucet and other bathroom fixtures, a manufacturer of electrical power products, an airline and many more.
Due Diligence, for purposes of a trademark search, includes searching for live and dead marks, and how litigious the mark holders are even if they are not in the same market. "Patent trolls" are individuals or entities that have multiple patents and do not implement them, only surveying the market to sue other companies they feel might be infringing. The results of a particular trademark search might reveal that a company with the same or substantially similar trademark might commonly bring suit against similar and not so similar marks. Even if the suit has little merit, it must be defended. The presence of a "trademark troll" with the same or similar mark can result in a large amount of legal fees.
Due Diligence also includes researching the dead marks and inquiring whether the marks are still used. A "dead" trademark does not mean it is no longer being used. It only means that for one reason or another, the registration was not maintained. This could result from the company making a mistake in the renewal process, the mark being cancelled, or a number of other things. It does not necessarily mean that the mark is no longer being used in commerce.
Search Engines are also powerful tools in determining whether an entity is using a trademark in commerce. There are a multitude of small businesses that do not register or seek to register a mark, but nonetheless conduct business with a particular trade name. They could have common law rights in a particular mark that could not be revealed without using a search engine.
While it is possible for an individual to do their own trademark search to determine whether a prospective trademark would pass muster with the USPTO, an attorney is the most adept at using various methods to determine the risk of litigation when attempting to protect a particular mark.