Me. Rev. Stat. tit. 12, § 10753

An applicant for a license or permit under this Part is responsible for submitting proof of residency to the agent or the department, or both. A resident license issued to a person unable to meet the residency requirements at the time the license was issued is invalid and must be returned to the commissioner upon request. A resident license is valid as long as the license holder continues to satisfy the residency requirements set out in section 10001, subsection 53 and the license is not revoked, suspended or otherwise invalid under this Part.