Md. Code, Transp. § 13-423

(a) Each motor vehicle for which a permit is required from the Public Service Commission under § 9–201 of the Public Utilities Article shall be registered under this title. (b) Each motor vehicle used in the interstate transportation of passengers for hire shall be registered under this title. (c) The owner of a motor vehicle specified in subsection (a) of this section when registering or renewing the registration of the vehicle shall: (1) Secure a permit from the Public Service Commission, or other appropriate agency, to operate on the highways; (2) Present the permit to the Administration; (3) Make application for registration or renewal of registration as required by the Administration; and (4) Pay to the Administration all applicable fees required for registration under this title. (d) No portion of the registration fee or other fees paid on vehicles required to be registered under this section will be refunded for any part of the year during which the vehicle is not used, unless pursuant to an order issued by an agency of the State or the United States government, the owner of the vehicle discontinues operation of the vehicle. If operation is discontinued a person may, at any time on or after the effective date of the order, surrender to the Administration the registration plates issued to the vehicle and apply for a refund of the registration fee paid for the vehicle prorated for the unused portion of the registration year.