Boston Understories looks at spaces and activities under highway viaducts through the lens of the regulatory sign. Standard markers like the ubiquitous ‘no trespassing’ have been used to limit or narrowly prescribe public access and fail to reflect the actuality of these sub-infrastructural spaces, where the market forces development into infrastructural margins, ecological systems converge with mobility networks, and public works intermingle with public recreation. Boston Understories reflects on these phenomena and introduces a new, more plural taxonomy of signs to encourage, amplify, and make legible actual and imagined collective domains of urban viaduct spaces