The provisions of Section 81-42 (Retail Continuity Along Designated Streets) shall apply within the Penn Center Subdistrict. However, the requirement that at least 50 percent of the street wall surface of each ground floor establishment be glazed with clear, untinted, transparent material, and not more that 50 percent of such transparent surface be painted or obstructed with signs shall not apply to any informational signs or marquees provided to identify rail mass transit or subway entrances in accordance with Section 81-52 (Sign Regulations).