The station controlling distress traffic may impose silence. They reserved the proword SEElONCE MAYDAY. It means forbidden to transmit! To cancel radio silence is proword SEELONCE FEENEE.
If you are close to the distress case and belief that to impose the radio silence is essential, you must use proword SEELONCE DISTRESS.
Example:
All ships,
All ships,
All ships
this is
Humber Coastguard, Humber Coastguard, Humber Coastguard,
Seelonce Mayday,
I say again
Seelonce Mayday,
Time 2344 UTC,
OUT.
Proword Pru-donce indicates that complete radio silence is no longer required and restricted (limited) use of the frequency may resume, but immediately giving way to all further distress communications.