N.Y.C. Admin. Code § 27-386: § 27-386 Directional sign design.

Directional exit signs shall comply with all of the requirements for exit signs in section 27-385 of this article, and shall read "EXIT" with a horizontal arrow or arrows indicating the direction to the exit or exits. However, when the arrow is below the letters, the letters may be three and three-eighths inches high and nine-sixteenths inch strokes, except in buildings and spaces classified in occupancy group F where they shall be at least five inches high with nine-sixteenths inch strokes. The arrow or arrows shall be red.