What signal is used to describe the small craft warning?

The correct identification of the signal for a small craft warning is one red pennant displayed by day. This warning is essential for small craft operators to understand that conditions are hazardous and that they should exercise caution. The use of a single red pennant clearly communicates to mariners that the water conditions may be unsafe for vessels categorized as small crafts, which typically include smaller boats and recreational vessels.

In contrast, the other options represent different signals that do not indicate a small craft warning. For example, two red pennants are used for more severe weather warnings, while the white flag at night and the green light at night are unrelated to the specific warnings for small craft. Thus, the singular red pennant serves as a straightforward and universally recognized signal for warning small craft operators about potentially dangerous conditions on the water.