I would say trademark law is based upon the idea that marks exist to delineate between businesses. You can name your beachside restaurant “Shell” and use a she

I would say trademark law is based upon the idea that marks exist to delineate between businesses. You can name your beachside restaurant “Shell” and use a shell as the logo, and even apply for a trademark if you want. As long as you haven’t lifted the specific copyrighted mark itself, and you’re not drilling for or selling oil, you’re good to go. Both of you have the ability to use the word “Shell” and (differing) images of a shell as a logo. This is an @ symbol used for a social media site, and a different @ symbol used for an online pharmacy as far as I can tell.