James Blakely wrote:

Has anyone heard the compassion call sign on the radio?

Yes, I've flown as Compassion and even Lifeguard. The Compassion callsign
requires that you be on such a mission (Angel Flight, AirLifeLine, etc.) and
when filing your flight plan you drop the first few characters of your call-sign
in favor of "CMF". So if you normally file as N376ES, you'd become CMF6ES, or
Compassion Six Echo Sierra.

I used Lifeguard right after 9/11, attempting to fly a trauma surgeon
coordinator up to Teterboro, New York - I would have been one of very few
airplanes airborne near Ground Zero at that time, as it was just a few days
after the attack. Unfortunately my airplane's landing gear decided on that day
not to retract after takeoff, so I was unable to complete the mission.

-Ryan