Good question! I choose to display them at my dojo so that people can see what I have done over the years- as a form of marketing only. I don't display them all-just the ones that are pertinent (dan certificates). I realize it is a double edged sword but I teach for a living and in this day and age people want to see it.
I studied in a traditional Shotokan dojo for many years. Up to Black Belt we only did the basic kicks-front, side round, hook, cresent, etc. Nothing fancy.