We don’t see it too often, but occasionally TPI receives letters without stamps and the words “Frank Mail” written where the stamp would be.
Frank mail refers to a custom of providing free postage to members of congress and other elected officials. Many prisoners believe that they have “franking privileges” for various reasons, and we do sometimes receive these letters. However, there is no allowance by the postal system for such “Frank Mail” that prisoners or indigent persons sometimes use, and the letters likely have just slipped through the system unnoticed.