A.m.g Sicily Cover, Assistance Needed

I've got this A.M.G. cover, and the large A.C.S that is stamped twice diagonally confuses me.



What I can gather so far about this cover is:
it is from the Psychiatric Hospital of Pallermo.
it is to the president of the provisional administration
it is sent 5/20/1944

(ive opened it up and saw it was a letter of discharge for a patient and the arrival postmark was 5/23/44 in Trapani)

A.C.S kind of looks like the same color ink as the Hospedale Psichiatrico el Pallermo stamp so I'm wondering if A.C.S might be an italian medical acronym. I'm just guessing though, any help is appreciated.

Allied Control System ?
https://www.academiedephilatelie.fr...jeg_1509.pdf