Exploratory Quantitative Assessment of Signature Variability Related to Shift Duration Using the Signature Change Scale

Handwritten signatures retain their legal validity and play a central role in the forensic examination of documents. While it is recognized that signatures can be influenced by contextual and human factors, research on the systematic evaluation of signature stability within a structured and quantitative framework under prolonged professional shift conditions remains limited. The aim of this study is to identify the temporal pattern of signature variability over a 24-h shift and to systematically quantify this variability using a structured ordinal rating system. This prospective observational study included 25 emergency department resident physicians working on a 24-h shift system. Handwriting samples were collected from the participants at the 0th, 8th, 16th, and 24th h of their shift. The signatures were evaluated using the Signature Change Scale, which assigns an ordinal score on a 0–5 scale, with each participant’s baseline (0-h) signature serving as the reference. The evaluations were conducted under double-blind conditions by two independent experts, each with over 10 years of experience in forensic document examination. In order to assess reliability, the inter- and intra-observer reliability were calculated. Inter-observer reliability was assessed by comparing the scores assigned by two independent raters for the same signatures. Intra-observer reliability was determined by re-evaluating the same anonymized dataset under the same conditions. Statistical analysis was performed using descriptive statistics, Wilcoxon signed-rank test, and intraclass correlation coefficient (ICC) analysis for reliability assessment. It was observed that signature deviation scores varied across time points. At the 8-h mark, mild deviation was detected in 84% of participants. By the 16th h, the frequency of higher deviation categories had increased; by the 24th h, mild deviation was observed in 60% of participants, mild-to-moderate in 32%, and moderate in 8%. It was noted that average deviation scores increased up to the 16th h, with no further significant increase observed between the 16th and 24th h. The inter- and intra-observer reliability ranged from 0.89 to 0.97 and 0.85 to 0.93, respectively. These ICC values indicate that inter- and intra-observer reliability was at a good to excellent level. A 24-h shift duration was observed to be associated with intra-individual variability in signature characteristics under controlled professional conditions. High inter- and intra-observer reliability observed under blind and repeated evaluations suggests good scoring consistency within the controlled conditions of the present study. The findings suggest that signature characteristics may exhibit context-sensitive variability influenced by individual and environmental factors. The Signature Change Scale should be regarded as an exploratory methodological framework only, and further studies with larger samples and comprehensive content, construct, criterion, and external validity analyses are required before any forensic or practical application.