AF1 call sign
Since Danny has locked the other site on this subject on Rumours & News, I have an interesting observation by a senior FAA employee who doesn't want to be known.
He says:
"When the BA pilot asked on the open frequency if he'd just seen AF1 there was long pause and the AFI pilot -- or someone on the frequency -- replied, "gulfstream five". also kinda makes sense....travel in trail with another aircraft with your transponder off and let the other flight handle everything in terms of communcations. AF does it all the time with formation flying so the multiple transponders do not confuse ATC. everyone stays on the same frequency to hear the controller but only one acknowledges it. S2800 would square with SAM 28000."