Brands distinguish your goods or services from those of your competitors. You cannot own a brand if you allow others to use similar brands. To be more precise, your brand stops being distinct.
Once you’ve found someone who is using a similar brand, you have to decide how you are going to handle this. An initial consideration is what parameters are you willing to accept? For example, are you only going to pursue companies using your EXACT name in connection with IDENTICAL goods or services? Maybe you don’t care if you find uses in certain geographic zones (e.g., west of the Mississippi). If the third party is inside your parameters, how do you begin enforcing your rights. This is a very deep topic, but for now it is enough to say that you do not have to start with a lawsuit, or even a cease-and-desist letter. Experienced counsel can evaluate your situation and help you select a path that is right for you.
I like to think of brand protection in terms of real property. Enforcing a brand is much like calling the police when you find a trespasser, or even evicting a tenant who has violated his lease. There is no sense in owning real property if you don’t stand up for your rights. It amazes me how often people begin building their business on top of a brand they don’t care to protect.
I don’t expect entrepreneurs to know trademark law or how to protect their brands; that’s my job! All I need you to know is that your brand is important to you.