Why perform a trademark search/pre-screening?
By performing a trademark search your aim is to discover if any trademarks are in existence, which may be relevant to your choice of a mark or affect the outcome of your own trademark application. Based on the trademark search results you will be able to determine whether or not your mark is cleared for registration (registerable).
You need to know if your mark is under a federal registration (covering all fifty states), state registration, or is in the process of being considered to be eligible for registration. You also need to know whether your mark is protected by any common law rights. You should avoid using a mark that is similar in appearance and sound to a mark that is currently registered or protected by a common law right. Since there is federal, state, and common law means of protecting marks, one has to search all thoroughly to determine whether a mark is cleared for registration. If you do not see your mark identifying a good or service for sale in a store, on the Internet, or elsewhere in the public domain, it does not mean that such mark is cleared for registration. Someone may have an interest in a particular mark whether regional, national or even broader. Your goal with a trademark search is to have a full understanding of the federal, state, and common law rights and any marks in the process of being registered, which may have a bearing on registerability of your mark.