Mont. Code Ann. § 61-3-405

An applicant for personalized license plates shall file an application in the form and by the date the department requires indicating the combination of letters or numbers, or both, requested as a registration number. There may not be a duplication of registration numbers, and the department may refuse to issue any combination of letters or numbers, or both, that may carry connotations offensive to good taste and decency or that are misleading or a duplication of license plates provided for elsewhere in this title.