Journal of the American Society of Questioned Document Examiners
Vol 23, No. 2, December 2020
Yan Wen, Crystal Tan, Hui Ying, Yvonne Sim, Chin Chin Lim, Chiew Yung Yang
Company stamps or seals are commonly used to authenticate official documents such as quotations, sales invoices, and employment or business contracts, or to demarcate an area on a document for a signatory to sign. Although the stamp is usually machine-made, the act of manual stamping by a person introduces variation in the orientation and position of the stamp impression relative to other elements (e.g. printed text or border) on a document.
Stamp impressions are sometimes encountered in documents submitted for analysis. In a suspected case of fraud or forgery, one of the things the document examiner would determine is if the stamp impression(s) on the document is physically stamped or a reproduction of another stamp impression. The features, characteristics and placement of the stamp impression(s) would also be examined.
In cases where multiple stamp impressions on several reproduced documents appear to have the same relative positioning (placement) and orientation to the other elements (e.g. signatory line) on the document, the document examiner has to consider the possibility that these stamp impressions could either be a result of cut-and-paste manipulation (hence not a product of an inking process) or original stamped impressions that match by chance i.e. random chance matches.
Preliminary findings from our previous research showed that the probability of random matches for original stamp impressions made using a circular self-inking stamp was 0.1% when the stamp was not oriented based on any specific marking, and 4% when the stamp was oriented with the ‘star’ symbol located at the 6 o’clock position. The current proof of concept study further examines stamp impressions made by one of the authors deliberately aligning and orientating the stamp in a specific way on a document. Factors such as the shape of the stamp die, stamp housing, and the presence of a signatory line were also considered. The percentage of stamp impressions that had matching relative position and orientation was found to be between 0.08 and 0.69%. This exploratory study suggests that when stamp impressions encountered in more than one reproduced document have similar placement and orientation relative to other elements in the document, the examiner needs to objectively consider whether they were made by “cut-and-paste” manipulations or a chance occurrence. In view of its practical potential, more representative and comprehensive data will be collected by extending this proof of concept study to more participants and a more detailed examination of the factors involved in stamp impressions.