Ala. Code § 45-1-81.03

To prevent motor vehicles from escaping taxation and to provide for a more efficient procedure for assessment and collection of taxes due on same, no licenses shall be issued to operate motor vehicles on the public highways of this state, nor shall any transfer be made by the judge of probate until the ad valorem tax on such vehicles shall have been paid to the county for the preceding year as evidenced by receipt from the judge. Every person, firm, or corporation driving or owning a motor vehicle who desires to operate a motor vehicle on the public highways of Alabama shall first return such motor vehicle for ad valorem taxation purposes to the judge of probate who shall issue a certificate of assessment on a form prescribed by the State Department of Revenue, shall collect the taxes shown thereon, and shall make a duplicate of the tax receipt and keep same on file in his or her office. The license tag shall be evidence of the payment of the license and ad valorem tax due as provided under this subpart.