Late response but here goes.
MARS does encrypt messages sent via 110A (PSK) often. The sig in question is MFSK, not PSK and dunno if MARS related.
MARS was told to stop using HAM modes and use 110A and similar NATO STANAG modems for interoperability with mil units but the use of HAM modes persists. The neat thing about 110A is it sets itself up for you to decode as long as you have it tuned in within 100Hz, then just watch the messages, if you see a uuuuu string, encrypted comms will follow.
Some info on MARS encryption;
The American Radio Relay League (ARRL) is the national association for amateur radio, connecting hams around the U.S. with news, information and resources.
www.arrl.org
This is an encryption app used by MARS in the past, dunno if they still do;
gettens.online