1. An automatic sorting machine for merging a postal article arriving in a stack and on edge in an ordered sequence of mail articles, wherein said automatic sorting machine comprises an image-taking apparatus for forming a digital image of said postal article including a postal delivery address, a monitoring and control processor for determining in said ordered sequence of mail articles a location at which said postal article is to be inserted in order to perform the merging on the basis of data produced in said sorting machine and of said digital image, and identification means controlled by the monitoring and control processor for generating an identification signal that visually designates said location directly in the stack so as to assist an operator with performing said merging, said identification signal being generated on the basis of data representative of the thickness of each mail article produced by said sorting machine, wherein said identification signal is a light signal and further including a light source of the laser source type disposed substantially above the mail articles, said light signal being aimed at one of the mail articles marking said insertion location.