How to have a trademark and keep it?

Im talking about a trademark something. Trademark perfume, balm flavor, ink color, phrase. For example, I used to always wear this perfume, hoping it would become my trademark. People would smell it in other places and remember me or say, Oh, this smells just like her!. But nobody seemed to notice that I always wore that perfume. And then, since Im still in school, I decided to use purple ink, and then I was the ONLY person in my grade who used purple ink. It started becoming my trademark, people would see something written in purple and they would say, Oh, its her paper. But then, another girl decided to start using purple ink, and everyone forgot it was my ink! I know it sounds silly, but I want something to be mine and only mine, my signature. My trademark! What can I do, that is not easily copied and is noticeable?