Technically, it could be possible to even use that card in a game, just by producing a signature. I can imagine a system, where both players have some LN channel and use such cards for playing, then the winner could get some satoshis from the loser.
Very interesting point of view and I include it in my to-get-involved-into things. However, I have some questions such as what if one player decides to leave the game without having any losses? What discourages them to leave instead of staying if they're losing?
Which problem do digital signatures resolve? I fail understanding the way you've thought this. Are we going to publish colored coins as cards or not?