A trademark does not have to be federally registered in order to be protected. In most cases, just having a history of using a trademark provides "common-law" protections.
So, why bother with the time and money involved in federally registering a trademark?
Trademark registration can also be acquired at the state level. State registration is only suitable for business that is conducted entirely in-state. The Department of Licensing and Regulatory Affairs (LARA), within the Secretary of State's office, manages trademark registration for the state of Michigan.