Whether you register your mark or not, it is up to you, the owner of the mark, to protect your brand.
Trademarks are “use it or lose it,” so if you stop using the mark in commerce, your rights can disappear.
It is also up to you to make sure others aren’t using your mark or a confusingly similar mark. If you allow someone else to use it (even unintentionally, because you didn’t notice) you can lose your trademark ownership, or they can ruin your mark by affiliating your mark with their less-than-great goods or services. Using the ® symbol (if you’re registered) or the ™ symbol (if you’re not) helps show the world that you consider it to be a valid, protected mark and that you will not hesitate to do what you need to do to protect it.
If you do notice someone infringing on your mark, the first recommended step is to politely get in touch with them, explain the situation, and ask them to stop. If they do not, it is a good idea to get a lawyer onboard to help you draft and send a cease and desist letter, which explains that what they’re doing is illegal, that you own the mark, and that they need to stop using it immediately or else you may be forced to bring legal consequences like a lawsuit.
Remember that you also need to make sure your mark doesn’t become so popular that it becomes generic!
If someone has accused you of infringing, or if you’re not sure whether you’re allowed to use a mark that you’d like to use, it’s a good idea to talk to a lawyer. They can help you do a search to make sure nobody else is using a confusingly similar mark. This is especially important if your brand is going to be a key piece of your business’s success, and/or if you’re about to spend a lot of time on branding, marketing, or product packaging. If a mark might be too similar, a lawyer can help walk you through the options that are best for you and your brand.