Me. Rev. Stat. tit. 24-A, § 2721-A

Whenever accident policies are effective immediately upon purchase, including but not limited to those policies purchased through coin-operated machines, there may be a provision included in the policy as follows: "If an accident policy or policies previously issued by the insurer to the insured be in force concurrently herewith making the aggregate indemnity for (insert type of coverage or coverages) in excess of $ (insert maximum limit of indemnity or indemnities) the excess is void and all premiums for such excess must be returned to the insured or to the insured's estate."