She, in turn, contacted Rol Murrow, who is the Chairman of the ACA. Rol indicated that as an ACA partner, pilots flying PNP missions are permitted to use the COMPASSION call sign. He stated that pilots should follow the procedures located on ACA's web site, which can be found at http://www.aircareall.org/callsign.htm.
Rol also added:
The call sign should not be used for positioning legs when animals are
not being transported - just for the group's animal relocation flight
From the attached Procedures document:
COMPASSION likewise has been designated to serve the public convenience, good,
and necessity and we strongly encourage pilots to adopt its use for public benefit flying
Hope this helps,