I would say there is a bit of an honor code. I’ve been in a performing duo for 6 years now, and while our name is unique, I can’t imagine someone taking it. One solution, without going through the process of trademarking it, is to establish a website right away. Even just purchasing the domain name (which is cheap) will help others from accidentally choosing the same name. I think in general, we as musicians want to have unique names so we’d rather not take one from someone else 🙂 (Not saying it can’t happen though…)