One of the survival signalling techniques taught by Hunter Safety/Education in Washington state is the three consecutive shot distress signal. The problem is twenty rounds of ammo can go pretty quick doing three shot volleys, plus the fact that you are putting lead in the air or at least discharging the firearm which presents additional risks. I gotta think a 100 pack of firecrackers would be less bulky and cheaper than 100 rounds of ammo, and accomplish about the same task. The SAR folks we talked to at the Mill Creek Watershed outside of Walla Walla still recognized the three shot distress signal as a legitimate method as of a few years ago.

I think generally anything in threes is recognized as some form of distress signal.