A saying needs to indicate source to be protected as a trademark
This may sound a little circular, but to be protected as a trademark, the word or symbol at issue needs to function as a trademark. That means it has to tell the consuming public that the good or service you sell in connection with the trademark comes from you.
A common pitfall is the ornamental use of a word or symbol. Let’s say you have a cool design or catchy saying, so you decide to put it on t-shirts and coffee mugs. That’s great, but it’s tricky protecting your words or design in that context as a trademark. Unless, of course, they actually function as a trademark by indicating source.
Think about where a brand appears on a t-shirt or coffee mug. On a shirt, it’s often on the inside tag or on a hang tag that’s attached to a shirt before it’s sold. On a coffee mug it’s usually on the side or even on the bottom. In both cases, the brand — the signal to customers who made the shirt or cup — takes a back seat to the catchy words or cool design that likely motivated the customer to purchase the item. If you want to protect those words or design as a trademark, you need to make sure they’re also displayed where the brand usually appears. As long as the words or design tell customers who made the good, it’s protectable as a trademark. Otherwise, the U.S. Patent and Trademark Office won’t register it, and a court won’t enforce trademark rights in it.
If your cool design or catchy saying doesn’t indicate source, you still might be able to protect it through copyright law or by getting a design patent — but that’s often a stretch. But one thing should be clear: you can’t protect it under trademark law if it’s just a decoration.