I can see it now. As I keep saying. The person who does not want to wear a mask just constantly pretends to eat and/or drink as flight attendant is approaching.
This "take mask off to eat or drink" thing basically kills the mask rule. For this to work we have to keep our mouths shut and covered and that includes not eating/drinking in flight and making it very clear the mask needs to be on at ALL times period.
I guess there are the few people who don't want to wear a mask, are not eating/drinking, and want to argue about why the rule shouldn't apply to them and maybe that is what this card is designed for. In that case you have an uncooperative passenger who is probably verbally abusive to the flight attendant and surrounding passengers and that should be dealt with immediately by police upon landing, not with a "yellow card."
Then there is the "small children and those with medical conditions may be exempt." They cannot require you to prove a medical condition. So that is another "get out of mask" method.
Maybe more strict mask rules IN the air terminal itself would translate into better compliance on the airplane. Yeah some airports are falling under the common mask in public places laws passed on the east and west coasts but there is a whole middle of the US with no such laws so no masks required in the air terminal.