an internationally recognised call for help

SOS is a Morse code distress signal used internationally, originally established for maritime use. Although SOS officially is just a distinctive Morse code sequence that is not an abbreviation for anything, in popular usage it is associated with phrases such as "Save Our Souls" and "Save Our Ship". Moreover, due to its high profile use in emergencies, the phrase "SOS" has entered general usage to informally indicate a crisis or the need for action.[1]

1. Wikipedia - SOS, visited 2020-03-11