License plate for a vehicle includes a plate having an indicia and arranged to be mounted on the vehicle, and a transponder arranged in the plate. The transponder is arranged to receive a signal from an interrogator, modify the received signal and transmitted the modified signal to the interrogator. The transponder may be a SAW transponder, an RFID transponder and/or include a reflective or back scattering antenna, a polarization antenna, a rotating antenna, or a corner cube or dihedral reflector. An energy harvesting component can be arranged on the license plate or in the license plate for providing power to the transponder. The energy harvesting component generates energy during or from movement or vibration of the vehicle.