For the OP, in my experience, as ever - 'it depends'.
We invariably used RFR callsigns for the transits - although in answer to Ex-Ascoteer, ATC occasionally tried to call us Ascot despite having RFR on the flight plan. Once at the venue it was down to the organisers who mostly referred to us by ac name. I never understood why our callsign system was so complicated, the JP pair often got called Lopblade!
I did an event at Ramstein, in a black Hawk, where I was directed round the houses via very detailed and unexpected taxi instructions, and finally ended up parking at the Blackhawk squadron - which turned out to have much better social plan than the main event.