The approval of the comprehensive plan, or of any amendment, extension or addition thereto, shall be by the affirmative vote of not less than a majority of the total members of the commission. Such approval shall be by a recorded motion which shall incorporate the findings of fact of the commission and the reasons for its action and the motion shall refer expressly to the maps, descriptive, and other matters intended by the commission to constitute the plan or amendment, addition or extension thereto. The indication of approval by the commission shall be recorded on the map and descriptive matter by the signatures of the chair and the secretary of the commission and of such others as the commission in its rules may designate.