Private lots must post signs at every entrance: tow operator name, phone, license number, and the rate. Signs must be visible and legible at night.
If you were towed from a lot with missing, illegible, or non-compliant signage, the tow may be illegal. Photograph the lack of signage at the time of pickup if possible.
Document everything. File a 311 / DCWP complaint. The fine and operator-level enforcement is real.
