Ref: MAYDAY RELAY
It is also internationally recognized and used.......in aviation and military.
As it is not in ICAO RT procedures or phraseology, I wouldn't bank on it being fully understood in the civil aviation arena worldwide. Native English speakers may put 2 and 2 together to get the '4' that you intend, but sticking to standard phraseology removes any guesswork and doubt, as well as making things clear for other listeners.