Trademarks are symbols, words, or combinations of words that are used to represent a product or a service. In order to obtain a trademark, you need to be able to show that the phrase has a “secondary meaning” that makes the phrase as you use it different from the usual meaning of the phrase. You will also need to show that the secondary meaning is connected with your product or service. Registering a trademark allows the person who registered it to control how the “mark” is used, protect their brand, and prohibit others from using the mark to sell their own products.

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A trademarked phrase identifies your specific product or service and distinguishes it from similar products or services [source: Simon]. In order to trademark a phrase, you must prove that the phrase has a secondary meaning that differs from its primary one and that the secondary meaning connects that phrase with your product or service

You register it with uspto.

Be aware that you cannot own the phrase. A trademark only gives you the exclusive right to use the phrase to identify your product. Someone in a different industry can use it freely.

You obtain enforceable trademark rights by being the first to use a distinctive brand on goods or services in commerce. Done.

Registration in the USA is entirely optional.

same way you trademark anything else.