This study draws on ethnographic and archival evidence from the Italian Archipelago of La Maddalena, offshore from the northeastern corner of Sardinia, where in 1972 the U.S. Navy installed a base for nuclear submarines. It addresses two questions: (1) How do non-experts make sense of radiological risk absent knowledge and classified information about its instantiations and consequences? (2) How do objectifications of risk change and stabilize within the same community over time? STS scholarship has emphasized the epistemic and relational dimensions of lay/expert controversies over risk assessment. Many case studies, mostly focused on the Anglo-Saxon world, have assumed lay and expert ways of knowing are incompatible due to clashing cultural identities. I use Keane's concept of “semiotic ideologies” and Peircean semiotic theory to critically reassess the validity of that assumption and examine the role of material evidence in processes of signification to explain how experts and non-experts fix, challenge, and negotiate the meanings of radiological risk in sociotechnical controversies. I critically review empirical studies and analyze ethnographic and archival data to advance a set of methodological and substantive arguments: meanings of risk change as new signs become available for interpretation; and meanings of risk are semiotically regimented: their emergence or silencing depend upon the power relations in place in a given community and organizational efforts to assemble coherent technopolitical arguments. I call this set of organizational practices “politics of coherence.”