I have created 6 cards to be used in the classroom to instruct the student's on what is expected of them for the use of cellphones and technology. I have made a RED light card, GREEN light card, and YELLOW light card with colored backgrounds for you to print in color and also, the same cards with no background color for you to print out on stock paper of your choice.
I use a magnetic clip to hang the card up on the Smart board. They are size 4" by 6" and work very nicely in the classroom. We review the positive behavior expectation for the classroom activity and the students visually use the card as a reminder if they can or can not use their phone, tablets, laptops.
This strategy works wonderful in the classroom.