In my younger days, there was a Pitts Special (?) in Canberra one day with the rego VH-XXX... What happened to it?
Rats, in your younger days (when your eyesight and memory was much better) you probably saw PTS2 VH-ZZZ.
On the OZ register there is a "Triple everything" except T & X.
As for not saying anything three times in a row over the airwaves, ICAO annex 10 volume II Aeronautical Communications, says.
With the exception of the telephony designators and the type of aircraft, each character in the call sign shall be spoken
separately.
Though a great many years ago (30+) on hearing a 'Triple' call sign on the radio, I looked it up in the AIP of the time, and it was a valid form of c/s.