One of the stumbling blocks for implementation of Vehicular Ad Hoc Networks is the penetration rate: the percentage of vehicles that have the communication equipment installed. As the equipment deployment is unlikely to happen instantaneously, it is important to explore the performance gains achievable at low penetration rates. This especially pertains to safety applications, which are expected to provide life-saving information to all drivers on the road within a given region. We propose a technique that can be employed by safety applications to address the low penetration issue. By using visual cues on the equipped vehicles, such as specific patterns of hazard warning lights, we show that for all but the lowest vehicle densities, a radio penetration rate of 30% is sufficient to inform more than 95% of drivers in the region of interest in a timely manner.