Mosses are dominant components of high-latitude environments, and Signy Island (maritime Antarctic) provides a representative example of polar cryptogam-dominated terrestrial ecosystems. In 2011, we mapped all moss banks, their characteristics (thickness, area, floristic composition) and investigated their relationship with selected environmental factors including topography (elevation, slope, aspect), biotic disturbance (fur seals), deglaciation age of the surfaces, location on the eastern vs. western side of the island and snow cover as a proxy of water supply during the summer (December). We here identify the most important environmental factors influencing moss bank characteristics and distribution and provide a baseline for future monitoring. Moss bank abundance and distribution are the result of the interaction of multiple abiotic and biotic factors acting at different spatial scales. The most important factors are the location of moss banks on the eastern vs. western side of the island at the macroscale (with thicker and larger moss banks and a prevalence of Chorisodontium aciphyllum on the western side) and their favourable aspect (mainly N, NW) at the microscale, providing better microclimatic conditions suitable for their development. The elevation threshold detected at 120 m could indicate the occurrence of a ‘moss bank line’, analogous to the tree line, and corresponds with a threshold of mean annual temperature of −4.8 °C. The other factors examined play a subsidiary role in affecting bank distribution and characteristics. These findings allow a better understanding of this key feature of maritime Antarctic vegetation and provide quantitative information about their ecology.