https://4n6.com/handwriting-and-forgery-examination/

Handwriting and handprinting identifications have been performed since the late 1800’s. Since each person’s handwriting and handprinting habits are unique, it can be established whether someone wrote a certain word, initials, signature or document. In order to do an accurate comparison with either handwriting, handprinting or signatures, it is necessary to have several known, unquestioned standards. A comparison is then made between the known standards in order to establish that the writings are consistent, replete with individual handwriting habits and identifiable with each other. If all three criteria are met and the questioned writing is contemporaneous to the known standards that are supplied, a positive identification of authorship or non-authorship can normally be made.