This paper argues that where appropriations or invocations of the past have contributed to projects of social and political change, they have usually done so with little or no recourse to the historical past. Instead, activists and campaigners have used various forms of vernacular past-talk to unsettle those temporary fixings of ‘common sense’ that limit thinking about current political and social problems. The example of such past-talk discussed here is the work of the art-activist collective REPOhistory, which sought between 1989 and 2000 to disrupt the symbolic patterning of New York’s official and homogenized public memory culture by making visible (‘repossessing’) overlooked and repressed episodes from the city’s past. In effect, they challenged the ways in which history’s dominance of past-talk within the public sphere was constituted by exclusions of subjects on grounds of gender, ethnicity and socio-economic status. REPOhistory fused politically-engaged art practices with Walter Benjamin’s belief in the redemptive potential of dialectical encounters between past and present. To assess the value of their art-as-activism projects (“artivism”), this article will situate REPOhistory’s practices within a frame of ideas provided by Benjamin, Jacques Derrida, Ernesto Laclau, and Chantal Mouffe. In a series of street sign installations that mixed visual art, urban activism, social history, and radical pedagogy, REPOhistory exemplified why the past is too important to be trusted to professional historians.