The sign M157 occurs with remarkable consistency at the Proto-Elamite tablets, especially at Susa. Its repeated appearance strongly suggests that it was not a decorative or incidental mark, but rather a structural component shaping how these early documents were arranged. Scheil proposed that M157 might correspond to the Proto-Cuneiform sign DUB (“tablet”), a simple descriptor for the clay document itself. While such a reading offered a preliminary explanation, it fails to capture the broader significance of the sign within the Proto-Elamite administrative and economic system. In this study, we reassess the function of M157 by integrating conventional philological methods with computational approaches. Drawing on the CDLI corpus, we examined both the frequency of M157 and its co-occurrence with other signs. The analysis shows that M157 frequently appears in close association with numerical systems and terms designating commodities, rations, and institutional units. This pattern indicates that M157 was embedded in accounting procedures rather than functioning merely as a title. Network analysis further confirmed its centrality, revealing that M157 acted as a hub connecting otherwise separate semantic clusters and thereby imposing an overarching structure on the texts. To test these insights, we employed machine learning techniques. A Support Vector Machine (SVM) was used to classify tablets by type, while a Long Short-Term Memory (LSTM) model predicted missing signs on fragmentary examples. In both cases, M157 emerged as indispensable for accurate categorization and reconstruction, reinforcing the idea that it was a structural marker with meta-textual value. Taken together, these results suggest that M157 functioned as a “meta-marker,” standardizing the layout of administrative records and reinforcing their institutional legitimacy. Rather than denoting simply “tablet,” M157 may have pointed to an archival convention, an organizational category, or even a specific institutional identity. Future research should pursue comparative work with Proto-Cuneiform material from Uruk to assess whether M157 represents a uniquely Proto-Elamite feature or part of a broader Near Eastern trend toward administrative standardization.