Describe and provide access to sensors in public spaces openly and visibly.
In the TransparenZH project with the City of Zürich, a previous startup I worked with explored methods of how to communicate effectively about the use of sensors in public spaces.
A set of decals was deployed around town, next to the location where sensors were active. These had a QR code, through which passers-by could access a realtime dashboard with the actual sensor data. See https://www.stadt-zuerich.ch/prd/de/index/stadtentwicklung/smart-city/transparenz.html It should be open source, and well adaptable to the needs of Basel City residents.
I would first check with the city authorities if a similar solution already exists or is in the works. There is also applicability in non-government sensors, such as run by companies, communities, or even private individuals.