Maybe custom blinking shoes like what they used to make for kids back in the day? Just mimic the blinking pattern.

There are many people who still wouldn’t notice until the siren comes on though. I can spot an interceptor if the sunlight just happens to hit it right, yet my mom will drive right past a parked white cop car with lights on and be surprised when I told her she didn’t slow down to pass it. Then if an emergency siren goes off she panics and tries to pull to the shoulder without locating the emergency vehicle when fully blocked in by other cars and only moving enough to block the ambulance driving along the shoulder.