This idea gets passed around on Pinterest a lot, probably because it is so simple and so cool.
I think this project would make the perfect gift from your church or youth group to give to your graduating seniors. Just get some plain white mugs from the dollar store. Let everyone write an affirming message to the person on the mug with a sharpie (and, if doing a lot of these, be sure to write the person's name on the side or bottom of the mug). Then, you bake the mugs in the oven for thirty minutes at 350 degrees and "Pesto!" -- the writing is permanent and you have the perfect gift for your graduates to drink coffee, tea or cocoa from as they start the next step in their journey of life and faith.