Before fingerprints, retinal scans, or DNA, our signatures served as our identifying “mark” for thousands of years. As we progressed from stone to papyrus to paper, the signature has served to recognize artists, solidify contracts, and communicate the personal messages of writers. Now that pen and paper are being replaced by computers and software, one would think that the handwriting expert (AKA Forensic Document Examiner) would lose his place in the world of forensics.

Enter the digital signature pad…

Now, instead of referring to the signature as a mark, we have a new name for it—biometric identifier. In many venues, electronic signature capture devices have replaced paper as the collector of his personal identifying mark which now includes the speed, direction, and intensity of an individual’s signature, his biometric data. The three-dimensional image on paper that document examiners analyze under lighting and magnification is now being recorded in digital form.

A Brief Review of the Process
Using an active electromagnetic digitizing pen and tablet or stylus (pen) and pressure-sensitive pad, users sign their name to an electronic document. The signature pad represents the “xy” coordinates of a graph. The pad senses the electro-static presence of the stylus. As it “writes” the signature, the software records its location at regular intervals, most commonly every 1/100 of a second.

Signature data is stored as encrypted data which contains the precise path of the pen or a signature image and summary biometric measurements.¹ The resulting progression of coordinate sets, when charted on a graph, provides the document examiner with a virtual map of the signature. It also defines the speed with which the signature was written by virtue of the distance between recorded locations. Some pads also record a “z” coordinate which correlates to the amount of pressure applied to the stylus.

The Future of the Forensic Document Examiner
After more than 90 years of relying on their skills and experience to help identify handwriting, are forensic document examiners now going to be replaced by computer code and digital readouts? Not yet.

As long as the signature is used as a biometric identifier, it will continue to be analyzed in the traditional manner. Since the files that are embedded in the document can be extracted and translated into handwriting, they can be analyzed just like inked signatures. Unlike the inked signature, however, raw data does not replace the three-dimensional flow of original handwriting which, by all professional accounts, is unique unto each writer. Instead, the examiner must analyze the resulting handwriting “graph” as she would a photocopy or similar two-dimensional rendering.

On the other hand, our new-found friend, the digital signature pad has provided the document examiner with a new source of measurable identification information which can be included as scientific data in a forensic report. From this data we can glean an important piece of information that could be previously inferred, but not precisely measured—the total time of execution and the individual segment (stroke) timings. For the first time in FDE history, the document examiner has a precise expression of the handwritten signature to analyze both mathematically and by applying the time-tested tenants of handwriting identification.²