Note 17 at 2 Th. 3:17: Communications in Paul's day were nothing like what we have today. It was easy to forge letters and it could take months or years to learn of a forgery and take measures to remedy the situation. Paul spoke of others forging letters in his name in this very epistle (2 Th. 2:2). Therefore, Paul had a special way of authenticating all his letters.

Paul usually dictated his letters to someone who wrote them, much like a secretary today. At the close of each letter, he would write a salutation in his own handwriting. This is what he was referring to here and was his token in each epistle.