Taken from a book called "Geordie, Fighting legend of the SAS"

[Joe Chi Minh]

by Geordie Doran with Mike Morgan:

There was at that time an SAS rear HQ situated on the island of Labuan, about 350 miles away. We received many signals from rear HQ, some of which seemed to be about nothing and were entirely surplus to requirements. Each signal had a reference number to be quoted on any reply which, in turn, also had a reference number. On replies to the "nothing" signals we appended our reference, YPMO - meaning literally 'You piss me off!' I don't know if HQ ever figured out what YPMO stood for, but "nothings" kept coming, and I think we reached YPM0/30 by the time I left!"