OK, at our Moderator's request, I shall expand my discussion of the Rail Travel Card.
Yes it was a paper ID card issued by an outfit called the Rail Travel Credit Agency with offices in Chicago Union Station. Presumably they made a credit check of applicants, but somehow i don't think it was too extensive. When I got mine during 1968, I essentially had no credit, not bad credit or good, just none. I was single and a Buck Sergeant in the Air Force; this is when I literally was "begging' in my Class A uniform to the manager at the Hill AFB bank to give me a Bankamericard (Visa). He did, but with an extremely low limit ($500; quickly raised when they learned i was a "good boy'). They simply didn't emboss on the spot major credit cards for college Freshmen the way they do today (or is it more a case of the way they DID pre Sep 15?).
Yet the RTC just showed up in the mail!!!
Now was it a credit card that would send you a monthly statement that you would pay in accordance with the agreed terms? Not quite. It simply meant that the holder had a "house account' with all of the participating roads which would individually bill you for charges on their road. The roads didn't seem to care how small the bill was. It still came with a heading such as "To: The Union Pacific Railroad Company; Dr. such was for a Salt Lake to Ogden trip. What if the road that sold you a ticket and the road operating the Diner were two different roads? well two bills, one for your transportation and another for your meals. Example, you bought a ticket to ride the CZ in Chicago and used the card for meals . The CB&Q would bill you for the ticket (rail and Pullman), but say the Diner on your CZ was a WP car? well you would also have a bill from the Western Pacific.
As Mr. Radzivanas notes, some roads such as the New York Central had had "enough" by the later 50's. They accepted American Express for a while, then scuttled that, but then later started accepting a regional card called Midwest Bank Card (hey, you live in New York - you got one of those?).
But somehow the card hung on into the Amtrak era, but by the time that Amtrak had assumed the functions of ticketing during 1972, they started to accept "all majors" and the RTC was history.
I could expand the discussion noting the accounting treatment of RTC transactions but such might appear that i am writing a textbook on railroad industry accounting practices. Finally, I have located my RTC and, if anyone with scanning equipment desires to post an image of such here at the topic, send me a PM with your mailing address and I will make a Xerox (whoops Minolta) copy of mine and send it off to you. There is no private information on it whatever.