(1) Signs within six hundred and sixty feet of the nearest edge of the right-of-way lawfully erected and maintained which are visible from the main traveled way of the primary system within commercial and industrial areas on June 1, 1971 shall be permitted to remain and be maintained.

(2) Signs within six hundred and sixty feet of the nearest edge of the right-of-way which are visible from the main traveled way of the primary system within commercial and industrial areas whose size, lighting, and spacing are consistent with customary use as set forth in RCW 47.42.062 may be erected and maintained. Signs lawfully erected and maintained on June 1, 1971 shall be included in the determination of spacing requirements for additional signs.