A frequent request I receive is to compare two signatures to determine if they are of common authorship or not. This type of comparison is problematic because if any differences between the two signatures are observed it is not really possible to say if they are due to natural variation in the signature habits of one individual or if they are due to the signatures actually being written by two different authors.
To determine if a questioned signature is genuine, or not, it usually has to be compared with a set of known, genuine signatures from the individual concerned. This set has to be large enough to allow the range of variation of the writer to be established. For some individuals with a very limited range of variation in their signatures this set may only need to be a handful of signatures. However if the individual has a very wide range of variation in their signatures then a large number of comparison signatures, typically 20 plus may be required.
A one to one comparison may however on occasion yield some evidence that both signatures are of common authorship. If some subtle writing habits of an individual appear in both signatures this can be significant. These would typically be writing habits that a forger would be unlikely to replicate such as complex letter forms, distinct pressure patterns, slant patterns, arrangement, alignment, spacial habits and speed of execution. Both signatures would in essence have a similar balance of rhythm and form.
There is of course one scenario where no comparison signatures are required to give a strong opinion that a questioned signature is a simulation. This is where examination of the questioned signature itself yields conclusive evidence that it is a simulation.
In one such case below I was presented with a questioned signature on a letter purporting to transfer a piece of land from one individual to another. Examination of the questioned signature in isolation using various different lighting sources and also using infra red luminescence showed strong evidence that more than one pen had been used to create the signature. A second pen, of similar colour, had been used to touch up the signature and make it appear more like a known one. In addition there was clear signs of the individual letters having been written separately and “blended” together.
This examination allowed me to reach a conclusive opinion of non-genuineness based solely on the examination of the questioned signature.
If you have any suspicion concerning a document in your possession contact a reputable Document Examiner who can help you establish the authenticity of your document.