Flight attendant recognition?

Flew in first on Alaska last week for work, and saw a fellow passenger hand the FA a small white card when she was doing initial drink orders following takeoff. The passenger encouraged the FA to open it but she demurred, but seemed surprised and grateful. The FA seemed to know what it was in any case. Have flown Alaska many times and have never seen this happen. Curious if this is some sort of recognition system like the American Airlines Above & Beyond certificates?