When the students attend the monthly service, we iron a customized patch onto their t-shirt to show that they came.
I create a document in word using graphics, color text, and whatever I want! I can fit six patches to a page, then print with my inkjet color printer and cut them out. In this case, I have to print a mirror image (see the one with the piano - before it has been ironed on).
The students love to collect patches, and it is an easy way to encourage participation.