Background: Trauma scoring systems anticipate mortality and enhance triage for resuscitation and medical involvement. The Reverse Shock Index multiplied by the Glasgow Coma Scale Score (rSIG), calculated as systolic blood pressure divided by heart rate, and multiplied by the GCS score, is a practical trauma scoring tool. It uses available physiological parameters and enables straightforward calculations, especially in busy emergency settings. Objective: To assess the Reverse Shock Index (rSI) multiplied by Glasgow Coma Scale Score (rSIG) for anticipation of in-hospital mortality in comparison to Trauma and Injury Severity Score (TRISS) score in adult polytrauma patients. Patients and methods: This cross-sectional observational study was conducted at Suez Canal University Hospitals in Ismailia and involved 104 adult polytrauma patients attending the Emergency Department. The focus was to appraise the predictive value of rSIG for in-hospital mortality relative to the TRISS score. Results: Non-survivors exhibited significantly lower mean scores for GCS, rSI, Revised Trauma Score (RTS), TRISS, and rSIG compared to survivors (p < 0.001), while the average Injury Severity Score (ISS) was significantly higher in non-survivors relative to survivors (p < 0.05). At a cutoff value of 14, rSIG predicted mortality in polytrauma patients, reaching a sensitivity of 94% and a specificity of 71% (AUC = 0.928). Conclusion: The rSIG demonstrated significantly greater predictive accuracy for mortality across the entire study population. An rSIG value of <14 serves as a straightforward and timely indicator for evaluating mortality risk in adults with polytrauma.