All official traffic signs, signals and markers existing at the time of the adoption of this chapter shall be considered official under the provisions of this chapter; provided, however, that the City Council may by resolution or motion at any time have the official traffic signs, signals or markers removed or changed, or the same may be done at the direction of the Public Works Director; and provided further, that any additional official traffic signs, signals or markers erected, installed or painted shall first be authorized by resolution or motion of the City Council or by order of the Public Works Director.