Letters of urgency (4)
'letters of urgency' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for asap that I've seen before include "At one's earliest convenience" , "Notation meaning with minimum delay" , "Common acronym for quick-as-you-can" , "Notation meaning without delay, fast as you can" , "'At the earliest moment, initially (4)'" .)
(Other definitions for sos that I've seen before include "Mayday call" , "Distress call" , "Morse Code for help" , "Help with dots and dashes" , "request for aid" .)