If you or a vessel that you are approaching feels that a dangerous situation is developing, the danger signal should be sounded. The signal, which is 5 short horn blasts, alerts nearby boats that you don't know what their intentions are, or that you feel that there is a risk of collision.

Note: These are not the only rules concerning sound signals in restricted visibility; there are additional rules concerning sound signals that may be found in the Rules of the Road or in Chapman's Piloting.