Systems, assemblies, and methods for detecting changes in polarization states are described. Example systems may include a light receiving unit including a sensor and a receiving polarizer. The sensor is configured to sense light from a polarized light source deflected through the receiving polarizer by a light directing article. The sensor is configured to generate a signal indicative a received polarization state of light deflected by the light directing articles. Such systems may be coupled to vehicles and may be useful for sensor-detectable signs, indicia, and markings to facilitate automated or assisted vehicular transport.