Good question. Most of the time, you have to get a lawyer who is licensed in your state to represent you. That is not true with a trademark application. You can confirm that here: 37 C.F.R. §§ 2.17; 11.1; 11.14
A trademark applicant can be represented in the trademark application process by any attorney that is licensed and in good standing in any state in the U.S. I am licensed and in good standing in Tennessee, so I can represent you in your trademark application, no matter where you live. Which makes sense, because there are hundreds of thousands of trademarks registered every year, and they’re all in D.C. I don’t want to move to D.C. You don’t want to hire a high-priced D.C. law firm to help you protect your small business. I can do it from Nashville, Tennessee, and I’ll give it everything those firms could, no matter where you are.