Notwithstanding any other provision of chapter 47.42 RCW, signs may be erected and maintained more than six hundred and sixty feet from the nearest edge of the right-of-way which are visible from the main traveled way of the interstate system, primary system, or scenic system when designed and oriented to be viewed from highways or streets other than the interstate system, primary system, or the scenic system and the advertising or informative contents of which may not be clearly comprehended by motorists using the main traveled way of the interstate system, primary system or scenic system.