I was wrong

I finally got an answer on the MARC poster. It isn't a MARC poster.... it's a CSX poster. Hence, the wrongness of my suspicion that it was street activist art, counter propaganda.

Recently, the MTA received a number of inquiries from
MARC riders concerning the "Watch, Ride & Report"
poster which was commissioned by CSX last year.

MARC contracts with CSX for its commuter rail service
on the Brunswick & Camden Lines. Both lines are owned
and operated by CSX.

CSX displayed the poster at rail facilities during
the last year as part of its campaign to promote
passenger security awareness. You may consider
contacting CSX Corporate Communications to inquire
about its origin.

MARC did not post or distribute this poster.
Please note that the term "MARC Marshals" is a
phrase used on the poster named by CSX and is not
an official MARC program.

MTA Customer Communications

What's an old radical to do when business interests start co-opting old socialist and nazi art in a counter propaganda way. And when they do so using fake police forces. (So I was a little right)

I specifically asked MARC to provide me with a contact at "any other agency, business, or interest that may have posted this poster." Alas, what is clearly a form letter response didn't provide one, so I'll keep looking.