Section 193.2917 - Warning signs(a) Warning signs must be conspicuously placed along each protective enclosure at intervals so that at least one sign is recognizable at night from a distance of 30m (100 ft.) from any way that could reasonably be used to approach the enclosure.(b) Signs must be marked with at least the following on a background of sharply contrasting color: The words "NO TRESPASSING," or words of comparable meaning.
Amdt. 193-2, 45 FR 70409, 10/23/1980, as amended at 47 FR 32720, 7/29/1982