By and large visual semiotics still misses a comprehensive method for the analysis of sculpture. The paper demonstrates that sculptures have a peculiar plastic sign -the mass. Intrinsic to three-dimensional objects, the mass determines the forces of gravity and inertia possessing a potential to suggest connotations of the artwork. Taking as examples the large monuments built in Soviet Latvia in , the paper distinguishes among three categories of monuments -static, dynamic and ambiguous -which owe their particular characteristics to diverse exposure of the mass enabled by various constructive techniques. As iconic signs these monuments represent actual identities and events while the exposed mass, as a plastic sign, conveys additional connotations like stability, change, motion, standstill, slowness, speed enabling a more nuanced interpretation of the represented persons and events. As a physical property of objects mass can be evaluated by handling them directly but the public is supposed to look at sculpture not to touch and handle it. The current psychology of perception holds however that the perceiver goes beyond the information given in the visual input, the process of perception depends also on the perceiver's knowledge and purposes in the contact with reality. Ubiquity of outdoor sculpture suggests that our accumulated experience of 3D artistic objects can be embedded into the elaboration of the visual input thus the viewers can perceive the mass and enrich the interpretation of sculpture considering the meanings of this plastic sign.