I put them all on my front counter together, with the text pointing towards the students. That way, I can compliment or remind them and they can quickly get the card they need. They keep the card until the end of the period as either a visual "Keep it up!" or "Make a better choice.".
If they receive a Praise Card, they write their name on a slip of paper to be entered into a drawing for prizes. Before receiving a Reminder Card, they receive an "official verbal warning". If the warning and Reminder Card aren't enough, I go to my school's behavior intervention plan.
Good news update: I haven't written any referrals and it is 5 weeks into the year!
Do you have a behavior system in place that uses more than one of the students' senses to encourage good and curb undesirable behavior? I'm always looking for new ideas!