The era of city-scale sensing is dawning. Supported by new sensing capabilities, the capability to detect and measure phenomena throughout a large area will allow deeper insight and understanding into how cities work. The challenge of city-scale sensing is not limited to developing new sensing applications, however. A sensor must be installed in a location. It must be provided power, storage, and communications. All these tasks stand aside from the desired sensing effort, but are necessary nevertheless. In this demo, we introduce an initial prototype for a modular, city-scale sensing platform the signpost network. The platform, designed to be physically attached to sign posts throughout a city, reduces the burden for sensor and application developers by providing the necessary resources to modules attached to it. Power is provided by harvesting from solar panels with battery storage, with each module allocated a certain subset of the system energy. The signpost platform also provides data storage, long-range communication, data processing, module isolation, and an installation point for connected modules. The signpost acts as a modular base station for researchers, citizen scientists, and other interested parties to deploy custom sensors for applications such as pedestrian counting, air quality monitoring, and RF spectrum sensing at a city-wide scale.