Some rear car bike racks come with rear lights incorporated and you can place the license plate on it as well. The rear lights can also be purchased separately and installed. These are available from different manufacturers and some of the car bike rack producers are also offering additional rear lights for their specific bike rack models. So there actually is a safe solution   We also recommend getting a license plate holder which is provided by major car bike rack manufacturers such as Thule, 1up or others.  https://www.1up-usa.com/product/license-plate-holder-2/  https://yakima.com/products/safetymate-lighting-plate-kit .