The next two in the sequence being:
"Strike3" and
"Yer Out!"
For those of you who know the Pilot involved, it certainly was 3 strikes and yer out!
Callsigns are an ICAO thing, and you have to apply to a chap somewhere at Heathrow to get allocated an official callsign. I seem to remember they don't issue callsigns to individuals anymore, only to company or AOC holders.
In the case of Flying Clubs and stinking rich individuals, IMHO it smacks of 'trying to be better than your average Joe'. The Airlines and the military I can understand, but it's no better than those drivers who pay huge amounts to have a personalised number plate?