Every motor vehicle which is at any time used as a taxicab or which is intended to be used as a taxicab on any highway shall have painted thereupon in distinctive color and shall at all times bear the word “TAXI,” in letters having height of at least 4 inches and a width of at least 1 inch. The word “TAXI” shall appear on the front and rear of the body of the taxicab, and shall be so located that it shall be plainly visible from a height of 4 feet.