These posters are mentioned in my e-book "Hygge in the Classroom" available on Kindle now for only £2.99 or free through Kindle Unlimited! I talk about how students should take ownership of their own behaviour and actions and if this can be reinforced in a positive manner then all the better!
Each poster (A3 size) is displayed at the start of the day and left up throughout. Each poster challenges students to think about how they can be 'marvellous/terrific/wonderful/thankful/fabulous'.
Throughout the course of the day, if you, support staff, prefects, lunch time supervisors or, indeed, the students themselves, notice anyone being particularly good, they can note their name on a post-it and stick it on the poster.
A child should be chosen at the end of the day to photograph the poster so that you can keep a record of their achievements.