At an airport, a black-background sign displaying a single white number (for example, "4") typically indicates —

Why: FAA-CT-8080-2H Figure 65 ("U.S. Airport Signs") shows a black-background sign reading a single number — the standard FAA runway distance-remaining sign, showing distance remaining to the end of the runway in thousands of feet, distinct from the red/white runway-designation holding position signs shown elsewhere on the same figure.

• Confuses the distance-remaining sign with runway numbering; runway designators (e.g. "4," "22") are rounded magnetic headings used to name the runway, shown on the separate red/white holding position signs, not this black/white marker.
• Invents an aircraft-count function for this sign; its function on Figure 65 is showing remaining runway distance, not a traffic count.