I've never seen it, but it would be a nice "reminder" to use the "right" card!

I remember stopping at "the next" restaurant along the road for lunch a few years ago. I paid with my VI (usuallly I use AX) and a few days later, my UA dining said "You've got miles!" I had NO idea that it was a RN location. If I had used my AX, I would have received DL miles, but I'd rather have the UA miles. And if I paid with cash (of course) I would have received none!