Open Space signs. A sign on open space or other undeveloped property open to the public, requires no sign permit if the sign is less than 35 square feet in area. For purposes of this Section 5.2., open space shall mean undeveloped land available to the public at no cost, for passive recreation such as hiking, bird watching, fishing, photography, picnicking, cross country skiing, biking, horseback riding, or other activities which do not alter or disturb the terrain and at the same time to conserve natural and scenic resources, protect air, streams or water supply, and enhance the value of the land to the public.