Introduction

lthough signatures usually contain only relatively small amounts of handwriting they are often written in an individual stylised manner and a scientific comparison with appropriate specimen signatures can yield useful evidence of authorship. A lack of legibility in a signature is not a limitation provided that the writer produces signatures in a consistent manner.

Signature examinations generally involve the comparison of signatures which are specimen (provable) against questioned (disputed) signatures. Attempts are often made to produce forged signatures by copying the design of a person's genuine signature. This may be done by freehand simulation or by various tracing techniques. However it is extremely difficult for a forger to achieve both accuracy in the shape and proportions of a signature and also achieve the correct smoothness of the pen line. Normally a copy is made either by writing slowly to achieve accuracy (and therefore losing fluency) or by writing rapidly so that more fluency is obtained (and therefore losing the shape).

It must be noted that (due to the comparative nature of the process) it is not normally possible to compare signatures in different names. It is also rarely possible to identify the person responsible for a forged signature, as the natural handwriting characteristics of the writer are necessarily masked by having to copy someone else's style. However it may be possible to establish that a group of forged signatures were written by just one person.

The Technique
In a signature comparison the features of the questioned signature(s) - construction, shape, proportions and fluency - are assessed and then compared with the same features in the specimen signatures. An assessment of the significance of any similarities or differences that are found is then made.

In all cases it is important that a representative selection of specimen signatures is available so that the range of natural variation of the signature can be assessed. In particular the authorship of signatures of the elderly or of persons whose writing ability is impaired by factors such as injury, medication or intoxication may be difficult to establish because of the greater degree of variation that can occur. In such cases an effective comparison can best be made with specimen signatures which have been written under similar conditions and which are as near contemporaneous with the questioned signatures as possible.