Detection of vulnerable road users such as cyclists, and scooter drivers, constitute a challenge for automotive radars due to their low radar cross-section and strong clutter existing in urban environments. To address this issue, a semi-passive millimeter wave identification (MMID) tag has been proposed to enhance their detection. The tag consists of two Monolithic Microwave Integrated Circuit (MMIC) amplifiers connected between two antennas and to improve tag identification, spread spectrum sequences are used, such as Barker codes. A proof-of-concept prototype at 24 GHz has been designed, using a low-power blind-spot Doppler radar installed in the car as the reader. The experimental results derived from the measurements carried out with a tag attached to a scooter in an urban environment have been obtained.