Back in the days while I was still in the Air Force reserves, NYC used to allow us to ride the train for free. I don’t know the exact law or whatnot, but they’d allow me in for free most of the time.
If I was in uniform I’d just walk past the clerk and wave and they’d buzz me in via the “special entry” spot, other times they’d say “use the gate.” If I was in civilian clothing, I’d present my ID card and they’d wave me in.
Every once in awhile one of the clerks would say “this isn’t allowed anymore.” Though most of the time they’d just wave me in. Like I said, I don’t know if this was a law, official process, or just a courtesy. But since they told me I could do it with my Military ID card, why not?
It’s not a huge perk, but if serving the nation grants service members a free train ride, hell I’ll take it!