Hi. How interesting to learn that deBono's work is used in your workplace. I have used Six Hats as a teacher with my students when in the classroom.
We had no metric re: number of slips posted. Some months, the bulletin board was stacked with slips. Other months did not feature as many slips. Sometimes this was a function of the school calendar, e.g., December and March often had fewer as we were in session fewer days during those months due to breaks.
In my role then as a school leader, I modeled sharing my gratitude by ensuring that I posted at least 4 slips each month. I also put blank slips in staff mailboxes to remind staff and included an occasional reference to the GNH board in my weekly newsletter to staff. I also incorporated GNH into my everyday speech, e.g., saying to staff members, "Thank you for doing X and increasing my/the school's/our group's GNH."
The types of expression of gratitude ran the gamut. Many featured comments thanking a colleague for assistance with some task. Some comments referenced having received emotional support. Other slips focused on expressing appreciation for a special treat (e.g., a colleague bringing cookies to a meeting).
A brief section of the book, Accelerating and Extending Literacy for Diverse Students, by Michele Kane and Dorothy Sisk, features a photo of the GNH board, with an explanation of the process, and some teacher commentary. You can check it out on Amazon (pages 61 - 62).