Every sign erected pursuant to the preceding section shall bear the word “stop” in letters not less than six inches in height and such sign shall at nighttime be rendered luminous by steady or flashing internal illumination, or by a fixed floodlight projected on the face of the sign, or by efficient reflecting elements on the face of the sign. Every stop sign shall be located as near as practicable at the nearest line of the crosswalk on the near side of the intersection or, if none, at the nearest line of the roadway.