Step 1: First things first, you need a stamp.
Have you ever wanted to make your own?
Well, it's pretty easy to order a stamp. I ordered mine from iPrint.com (Trodat printy 4911 with a font size of 8).
This particular stamp has a window in front so that you can see where your stamp will fall but for a single line of text in the middle of the stamper, it is a little tricky to place it exactly where you want it.