On a corner lot where setback or side yard exists, no fence, wall, shrubbery, ground, sign, billboard, marquee, or other obstruction to vision between a height of 2 feet and 10 feet above the centerline grade of intersecting streets shall be erected, placed, planted, allowed to grow, or maintained within the triangular yard space formed by the intersecting street lines and a line joining points on such street lines 25 feet from the point of intersection of the streets. Public utility poles and existing trees trimmed from the ground level to a height of 10 feet shall not be considered obstructions to vision.