Sammy Arson, flirting with the hard left :3train guard asked for tickets, I showed my ITSO card expecting needing to wait for them to scan it and validate that I'd tapped in, they just go "yeah that's fine"
twice now that's happened (only ever needed to scan to prove once ever) 
one day I'll be brave enough to play the "show any vaguely rectangular thing to a guard and see if they assume it's a ticket" game
Klaus Frank@theresnotime Could work, but if it is an actual card used for tickets it is more guaranteed to work. But also if you do it you need to be 100% confident. Because they'll know when you're not sure themselves and double check then. (Also have the correct card with you to show immediately when they tell you it's the wrong one...)